From magnus at therning.org  Sun Nov  1 09:43:19 2020
From: magnus at therning.org (Magnus Therning)
Date: Sun, 01 Nov 2020 10:43:19 +0100
Subject: [Haskell-cafe] Hackage and searching for substrings
Message-ID: <87361tquo8.fsf@therning.org>

Just now I thought I'd check what kind of lib waargonaut is. Being lazy
I typed "waarg" into the package search box and found nothing!

Is there a way to make Hackage find waargonaut without having to type
the full package name?

/M

--
Magnus Therning              OpenPGP: 0x927912051716CE39
email: magnus at therning.org
twitter: magthe              http://magnus.therning.org/

It is better to keep your mouth shut and appear stupid than to open it
and remove all doubt.
     — Mark Twain
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From taylor at fausak.me  Sun Nov  1 13:12:44 2020
From: taylor at fausak.me (Taylor Fausak)
Date: Sun, 01 Nov 2020 08:12:44 -0500
Subject: [Haskell-cafe] 2020 State of Haskell Survey
Message-ID: <4b3bdfaa-125f-4a89-b60b-c12d44b99c06@www.fastmail.com>

Hi friends! I am very excited to announce the fourth annual state of Haskell survey. It opens today (the 1st) and stays open for two weeks (the 15th). I would greatly appreciate it if you could take 10 minutes to fill it out. Thanks!

https://haskellweekly.news/survey/2020.html

From fa-ml at ariis.it  Sun Nov  1 16:40:07 2020
From: fa-ml at ariis.it (Francesco Ariis)
Date: Sun, 1 Nov 2020 17:40:07 +0100
Subject: [Haskell-cafe] Hackage and searching for substrings
In-Reply-To: <87361tquo8.fsf@therning.org>
References: <87361tquo8.fsf@therning.org>
Message-ID: <20201101164007.GA14953@extensa>

Il 01 novembre 2020 alle 10:43 Magnus Therning ha scritto:
> Is there a way to make Hackage find waargonaut without having to type
> the full package name?

Not the same, but…
    https://html.duckduckgo.com/html?q=site%3Ahackage.haskell.org%20waarg

From magnus at therning.org  Sun Nov  1 17:09:26 2020
From: magnus at therning.org (Magnus Therning)
Date: Sun, 01 Nov 2020 18:09:26 +0100
Subject: [Haskell-cafe] Hackage and searching for substrings
In-Reply-To: <20201101164007.GA14953@extensa>
References: <87361tquo8.fsf@therning.org> <20201101164007.GA14953@extensa>
Message-ID: <87blghknqx.fsf@therning.org>


Francesco Ariis <fa-ml at ariis.it> writes:

> Il 01 novembre 2020 alle 10:43 Magnus Therning ha scritto:
>> Is there a way to make Hackage find waargonaut without having to type
>> the full package name?
>
> Not the same, but…
>     https://html.duckduckgo.com/html?q=site%3Ahackage.haskell.org%20waarg

Yes, that's certainly an option. Just that `!hackage waarg` would be a
lot nicer to write than `site:hackage.haskell.org waarg` :)

/M

--
Magnus Therning              OpenPGP: 0x927912051716CE39
email: magnus at therning.org
twitter: magthe              http://magnus.therning.org/

I am always doing that which I cannot do, in order that I may learn
how to do it.
     — Pablo Picasso
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From lemming at henning-thielemann.de  Sun Nov  1 17:34:35 2020
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sun, 1 Nov 2020 18:34:35 +0100 (CET)
Subject: [Haskell-cafe] Hackage and searching for substrings
In-Reply-To: <87blghknqx.fsf@therning.org>
References: <87361tquo8.fsf@therning.org> <20201101164007.GA14953@extensa>
 <87blghknqx.fsf@therning.org>
Message-ID: <alpine.DEB.2.20.2011011834010.6836@sputnik>


On Sun, 1 Nov 2020, Magnus Therning wrote:

> Francesco Ariis <fa-ml at ariis.it> writes:
>
>> Il 01 novembre 2020 alle 10:43 Magnus Therning ha scritto:
>>> Is there a way to make Hackage find waargonaut without having to type
>>> the full package name?
>>
>> Not the same, but…
>>     https://html.duckduckgo.com/html?q=site%3Ahackage.haskell.org%20waarg
>
> Yes, that's certainly an option. Just that `!hackage waarg` would be a
> lot nicer to write than `site:hackage.haskell.org waarg` :)

I guess you can configure your browser to expand the former to the latter.

From charukiewicz at protonmail.com  Sun Nov  1 18:37:51 2020
From: charukiewicz at protonmail.com (Christian Charukiewicz)
Date: Sun, 01 Nov 2020 18:37:51 +0000
Subject: [Haskell-cafe] Hackage and searching for substrings
In-Reply-To: <alpine.DEB.2.20.2011011834010.6836@sputnik>
References: <87361tquo8.fsf@therning.org> <20201101164007.GA14953@extensa>
 <87blghknqx.fsf@therning.org> <alpine.DEB.2.20.2011011834010.6836@sputnik>
Message-ID: <Ny6eGyX_8j_fITSvRvqceaXgkHfL5OfYfyv83QYAk_yYXZM9MXklq7AQFUsM3pTMld8P2gojwx5iWqfla5BRQn6XO8DsB4szTYzE7c2rJGU=@protonmail.com>

You certainly can. Someone gave a great example on Twitter of doing this for a custom GitHub search: https://twitter.com/HamelHusain/status/1307353823216762880

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐

On Sunday, November 1st, 2020 at 11:34, Henning Thielemann lemming at henning-thielemann.de wrote:

> On Sun, 1 Nov 2020, Magnus Therning wrote:
>
>> Francesco Ariis fa-ml at ariis.it writes:
>>
>>> Il 01 novembre 2020 alle 10:43 Magnus Therning ha scritto:
>>>
>>>> Is there a way to make Hackage find waargonaut without having to type
>>>>
>>>> the full package name?
>>>
>>> Not the same, but…
>>>
>>> https://html.duckduckgo.com/html?q=site%3Ahackage.haskell.org waarg
>>
>> Yes, that's certainly an option. Just that !hackage waarg would be a
>>
>> lot nicer to write than site:hackage.haskell.org waarg :)
>
> I guess you can configure your browser to expand the former to the latter._______________________________________________
>
> Haskell-Cafe mailing list
>
> To (un)subscribe, modify options or view archives go to:
>
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>
> Only members subscribed via the mailman list are allowed to post.
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From ietf-dane at dukhovni.org  Sun Nov  1 20:56:18 2020
From: ietf-dane at dukhovni.org (Viktor Dukhovni)
Date: Sun, 1 Nov 2020 15:56:18 -0500
Subject: [Haskell-cafe] Hackage and searching for substrings
In-Reply-To: <87361tquo8.fsf@therning.org>
References: <87361tquo8.fsf@therning.org>
Message-ID: <20201101205618.GN1464@straasha.imrryr.org>

On Sun, Nov 01, 2020 at 10:43:19AM +0100, Magnus Therning wrote:

> Just now I thought I'd check what kind of lib waargonaut is. Being lazy
> I typed "waarg" into the package search box and found nothing!
> 
> Is there a way to make Hackage find waargonaut without having to type
> the full package name?

Hoogle does the job quite nicely, and finds matches as you type:

    https://hoogle.haskell.org/

Just typing "waa" was sufficient to exclude false-positives.

-- 
    Viktor.

From duke.j.david at gmail.com  Sun Nov  1 22:05:23 2020
From: duke.j.david at gmail.com (David Duke)
Date: Sun, 1 Nov 2020 22:05:23 +0000
Subject: [Haskell-cafe] GHC-8.6.3 question.
In-Reply-To: <3cfda95bdc841d977c6300580628a82a@jackkelly.name>
References: <CAN7OfXTprjbV7sWiSF7K4rD6ns5Jv_shCj3PLwqVgQmbNQD15w@mail.gmail.com>
 <3cfda95bdc841d977c6300580628a82a@jackkelly.name>
Message-ID: <CAN7OfXR5sBpBSWu1dC_av6QkStsgeBf+A1q0r+zMJ8wQt8eoDA@mail.gmail.com>

Thanks Jack. I have  used ghcup previously but had forgotten  about it -
one problem solved!

regards
David

On Sat, Oct 31, 2020 at 8:38 PM <jack at jackkelly.name> wrote:

> Hello David,
>
> November 1, 2020 4:35 AM, "David Duke" <duke.j.david at gmail.com> wrote:
>
> > I'm in the process of having to reinstall ghc-8.6.3 in order to use a
> library (gtk) where the last
> > successful build is 8.6.3. I was able to do that on linux. However I'm
> now trying to repeat this
> > under OSX.
>
> I don't use macOS so I can't answer your build question directly, but do
> you use ghcup ( https://www.haskell.org/ghcup/ ) to manage your GHC
> versions? It looks like ghcup has been told about 8.6.3 on darwin:
> https://gitlab.haskell.org/haskell/ghcup/-/blob/8f4705a50eefafd92ceef32094eec7140885b3d5/.download-urls#L99
>
> HTH,
>
> -- Jack
>


-- 
David Duke
Emeritus Professor of Computer Science
School of Computing University of Leeds UK
E:duke.j.david at gmail.com
W:https://engineering.leeds.ac.uk/staff/334/Professor_David_Duke
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From magnus at therning.org  Mon Nov  2 13:23:31 2020
From: magnus at therning.org (Magnus Therning)
Date: Mon, 02 Nov 2020 14:23:31 +0100
Subject: [Haskell-cafe] Hackage and searching for substrings
In-Reply-To: <87361tquo8.fsf@therning.org>
References: <87361tquo8.fsf@therning.org>
Message-ID: <87wnz36gfg.fsf@therning.org>


Magnus Therning <magnus at therning.org> writes:

> Just now I thought I'd check what kind of lib waargonaut is. Being lazy
> I typed "waarg" into the package search box and found nothing!
>
> Is there a way to make Hackage find waargonaut without having to type
> the full package name?

Interpreting the responses so far I guess the correct answer to my
question is "no!"

/M

--
Magnus Therning              OpenPGP: 0x927912051716CE39
email: magnus at therning.org
twitter: magthe              http://magnus.therning.org/

Ah, good taste! What a dreadful thing! Taste is the enemy of
creativeness.
     — Pablo Picasso
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From andrew.thaddeus at gmail.com  Mon Nov  2 14:15:16 2020
From: andrew.thaddeus at gmail.com (Andrew Martin)
Date: Mon, 2 Nov 2020 09:15:16 -0500
Subject: [Haskell-cafe] Intention to take over the pipes-text package
In-Reply-To: <87v9esk5bb.fsf@devalot.com>
References: <87v9esk5bb.fsf@devalot.com>
Message-ID: <CABNC7eMpZNKyN_RaV-CnxTK1iM4Q9XsiZCVtUQQfFhZF14eV5g@mail.gmail.com>

For what it's worth, I took over some of Michael Thompson's other libraries
(streaming and streaming-bytestring) about two years ago. He is no longer
active on GitHub and was not responsive to email at the time.

On Thu, Oct 29, 2020 at 7:00 PM Peter J. Jones via Haskell-Cafe <
haskell-cafe at haskell.org> wrote:

> (This is a re-post from October 6, 2020 since the original did not make
> it into the archive.)
>
> The pipes-text [1] package on Hackage hasn't been updated in about 4
> years and doesn't currently build due to outdated `build-depends'.
>
> Patches have been supplied to the GitHub [2] repository but none have
> been merged.  The last commit was on Dec 2, 2016.
>
> I have attempted to reach out to the author (Michael Thompson) to offer
> assistance and have not received any response.
>
> As per the instructions on the Haskell Wiki, I'm posting this message to
> signal my intent to take over the pipes-text package as a maintainer.  I
> have a working fork here [3].
>
> Michael, if you prefer to keep the package under your control I'm more
> than happy to help you manage the GitHub project and get some patches
> merged.  Otherwise I'll reach out to the Hackage administrators after a
> reasonable amount of time has passed.
>
> [1]: https://hackage.haskell.org/package/pipes-text
> [2]: https://github.com/michaelt/text-pipes
> [3]: https://github.com/pjones/pipes-text
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.



-- 
-Andrew Thaddeus Martin
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From lysxia at gmail.com  Mon Nov  2 14:35:17 2020
From: lysxia at gmail.com (Li-yao Xia)
Date: Mon, 2 Nov 2020 09:35:17 -0500
Subject: [Haskell-cafe] Hackage and searching for substrings
In-Reply-To: <87wnz36gfg.fsf@therning.org>
References: <87361tquo8.fsf@therning.org> <87wnz36gfg.fsf@therning.org>
Message-ID: <eb6c2e93-15e9-7186-b4d6-d5bfc6a4a7d0@gmail.com>

Hi Magnus,

One approximation of that idea is to use hoogle:

https://hoogle.haskell.org/?hoogle=is%3Apackage%20waar

(note the "is:package" key to avoid looking for identifiers inside packages)

Li-yao

On 11/2/2020 8:23 AM, Magnus Therning wrote:
> 
> Magnus Therning <magnus at therning.org> writes:
> 
>> Just now I thought I'd check what kind of lib waargonaut is. Being lazy
>> I typed "waarg" into the package search box and found nothing!
>>
>> Is there a way to make Hackage find waargonaut without having to type
>> the full package name?
> 
> Interpreting the responses so far I guess the correct answer to my
> question is "no!"
> 
> /M
> 
> --
> Magnus Therning              OpenPGP: 0x927912051716CE39
> email: magnus at therning.org
> twitter: magthe              http://magnus.therning.org/
> 
> Ah, good taste! What a dreadful thing! Taste is the enemy of
> creativeness.
>       — Pablo Picasso
> 
> 
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
> 

From Graham.Hutton at nottingham.ac.uk  Tue Nov  3 09:52:19 2020
From: Graham.Hutton at nottingham.ac.uk (Graham Hutton)
Date: Tue, 3 Nov 2020 09:52:19 +0000
Subject: [Haskell-cafe] Journal of Functional Programming - Call for PhD
	Abstracts
Message-ID: <8C3FB908-F501-4AC7-88B1-FD032F9E86D8@nottingham.ac.uk>

Dear all,

If you or one of your students recently completed a PhD in the area
of functional programming, please submit the dissertation abstract
for publication in JFP: simple process, no refereeing, open access,
200 published to date, deadline 30th November 2020.  Please share!

Best wishes,

Graham Hutton


============================================================

CALL FOR PHD ABSTRACTS

Journal of Functional Programming

Deadline: 30th November 2020

http://tinyurl.com/jfp-phd-abstracts

============================================================

PREAMBLE:

Many students complete PhDs in functional programming each
year. As a service to the community, twice per year the
Journal of Functional Programming publishes the abstracts
from PhD dissertations completed during the previous year.

The abstracts are made freely available on the JFP website,
i.e. not behind any paywall.  They do not require any transfer
of copyright, merely a license from the author.  A dissertation
is eligible for inclusion if parts of it have or could have
appeared in JFP, that is, if it is in the general area of
functional programming.  The abstracts are not reviewed.

Please submit dissertation abstracts according to the instructions
below.  We welcome submissions from both the PhD student and PhD
advisor/supervisor although we encourage them to coordinate.

============================================================

SUBMISSION:

Please submit the following information to Graham Hutton
<graham.hutton at nottingham.ac.uk> by 30th November 2020:

o Dissertation title: (including any subtitle)

o Student: (full name)

o Awarding institution: (full name and country)

o Date of PhD award: (month and year; depending on the
  institution, this may be the date of the viva, corrections
  being approved, graduation ceremony, or otherwise)

o Advisor/supervisor: (full names)

o Dissertation URL: (please provide a permanently accessible
  link to the dissertation if you have one, such as to an
  institutional repository or other public archive; links
  to personal web pages should be considered a last resort)

o Dissertation abstract: (plain text, maximum 350 words; you may
  use \emph{...} for emphasis, but we prefer no other markup or
  formatting; if your original abstract exceeds the word limit,
  please submit an abridged version within the limit)

Please do not submit a copy of the dissertation itself, as
this is not required.  JFP reserves the right to decline
to publish abstracts that are not deemed appropriate.

============================================================

PHD ABSTRACT EDITOR:

Graham Hutton
School of Computer Science
University of Nottingham
Nottingham NG8 1BB
United Kingdom

============================================================




This message and any attachment are intended solely for the addressee
and may contain confidential information. If you have received this
message in error, please contact the sender and delete the email and
attachment. 

Any views or opinions expressed by the author of this email do not
necessarily reflect the views of the University of Nottingham. Email
communications with the University of Nottingham may be monitored 
where permitted by law.





From rae at richarde.dev  Tue Nov  3 18:15:19 2020
From: rae at richarde.dev (Richard Eisenberg)
Date: Tue, 3 Nov 2020 18:15:19 +0000
Subject: [Haskell-cafe] Tomorrow: Simon PJ announces Haskell Foundation
Message-ID: <010f01758f520a5c-ffadd00c-9d88-417b-b99d-5c948136bc2b-000000@us-east-2.amazonses.com>

Tomorrow (Wednesday Nov 4) at 12:00 UTC, Simon PJ will announce the formation of the Haskell Foundation, an independent, non-profit organization dedicated to broadening Haskell adoption. This will be a part of Haskell eXchange, but this announcement will be free to attend, via YouTube. Much of the presentation will be time for Q&A; questions can be posed both within the Haskell eXchange HopIn platform and via comments on YouTube.

Attend at https://youtu.be/MEmRarBL9kw <https://youtu.be/MEmRarBL9kw>

Just to forestall any disappointment: I won't be answering any questions here until at least after the announcement -- but do please come and ask questions there and afterwards.

Richard
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From mgajda at mimuw.edu.pl  Wed Nov  4 09:49:11 2020
From: mgajda at mimuw.edu.pl (Michal J Gajda)
Date: Wed, 4 Nov 2020 10:49:11 +0100
Subject: [Haskell-cafe] Looking for maintainers or comaintainers on my
	Haskell projects
Message-ID: <CACQVYRB7yU+KHO9n=YsruOy66c0jbgs5ctwhKAedULt8v+ogEQ@mail.gmail.com>

Hi Chris.,

> If you want to take xeno and make it into a publishable package, please do so.

We have offered to take over xeno over a year ago, and this offer still stands
backed by me personally. Since I have made a few contributions, you
may know that I would deliver here.

To add me as maintainer on Hackage: MichalGajda
To add me on GitHub: mgajda
-- 
  Cheers
    Michał

From rae at richarde.dev  Wed Nov  4 14:00:39 2020
From: rae at richarde.dev (Richard Eisenberg)
Date: Wed, 4 Nov 2020 14:00:39 +0000
Subject: [Haskell-cafe] Announcing the Haskell Foundation
Message-ID: <010f0175938f3c13-4a2fb1a4-40bf-4d14-abbb-e7ec70fc7add-000000@us-east-2.amazonses.com>

I'm very pleased to announce the creation of the Haskell Foundation (HF), an independent, non-profit organisation dedicated to broadening Haskell adoption.

Website: https://haskell.foundation/ <https://haskell.foundation/>
Twitter: @haskellfound
Founding whitepaper: https://haskell.foundation/whitepaper/ <https://haskell.foundation/whitepaper/>
Simon Peyton Jones's announcement, with lots of Q&A: https://www.youtube.com/watch?v=MEmRarBL9kw <https://www.youtube.com/watch?v=MEmRarBL9kw>
The "official" ask-me-anything on Reddit: https://www.reddit.com/r/haskell/comments/jnwg7i/haskell_foundation_ama/ <https://www.reddit.com/r/haskell/comments/jnwg7i/haskell_foundation_ama/>
Mailing list for future HF announcements: https://mail.haskell.org/cgi-bin/mailman/listinfo/hf-announce <https://mail.haskell.org/cgi-bin/mailman/listinfo/hf-announce>
Mailing list for HF discussion / involvement: https://mail.haskell.org/cgi-bin/mailman/listinfo/hf-discuss <https://mail.haskell.org/cgi-bin/mailman/listinfo/hf-discuss>

Please join the conversation. We need your participation to realize the vision of the foundation as *our* foundation, not *their* foundation.

Looking forward to seeing where this all leads!
Richard
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From icfp.publicity at googlemail.com  Thu Nov  5 02:56:11 2020
From: icfp.publicity at googlemail.com (Sam Tobin-Hochstadt)
Date: Wed, 04 Nov 2020 21:56:11 -0500
Subject: [Haskell-cafe] Call for Workshop Proposals: ICFP 2021
Message-ID: <5fa369cbc923a_5b58f2941638@homer.mail>

        CALL FOR WORKSHOP AND CO-LOCATED EVENT PROPOSALS
                            ICFP 2021
 26th ACM SIGPLAN International Conference on Functional Programming


                       August 22 - 27, 2021
                          Daejon, Korea
                    https://icfp21.sigplan.org/

The 26th ACM SIGPLAN International Conference on Functional Programming
will be held in Daejon, Korea on August 22-27, 2021, with the possibility
of a virtual conference. ICFP provides a forum for researchers and developers 
to hear about the latest work on the design, implementations, principles, and 
uses of functional programming.

Proposals are invited for workshops (and other co-located events, such
as symposiums) to be affiliated with ICFP 2021 and sponsored by
SIGPLAN. These events should be less formal and more focused than ICFP
itself, include sessions that enable interaction among the attendees,
and foster the exchange of new ideas. The preference is for one-day
events, but other schedules can also be considered.

The workshops are scheduled to occur on August 22rd (the day
before ICFP) and 26-27th of August (the two days after ICFP).

----------------------------------------------------------------------

Submission details
 Deadline for submission:     November 27, 2020
 Notification of acceptance:  December 15, 2020

Prospective organizers of workshops or other co-located events are
invited to submit a completed workshop proposal form in plain text
format to the ICFP 2021 workshop co-chairs
(Leonidas Lampropoulos and Zoe Paraskevopoulou) via email to

   icfp-workshops-2021 at googlegroups.com

by November 27, 2020. (For proposals of co-located events other than
workshops, please fill in the workshop proposal form and just leave
blank any sections that do not apply.) Please note that this is a firm
deadline.

Organizers will be notified if their event proposal is accepted by
December 15, 2020, and if successful, depending on the event, they
will be asked to produce a final report after the event has taken
place that is suitable for publication in SIGPLAN Notices.

The proposal form is available at:

http://www.icfpconference.org/icfp2021-files/icfp21-workshops-form.txt

Further information about SIGPLAN sponsorship is available at:

http://www.sigplan.org/Resources/Proposals/Sponsored/

----------------------------------------------------------------------

Selection committee

The proposals will be evaluated by a committee comprising the
following members of the ICFP 2021 organizing committee, together with
the members of the SIGPLAN executive committee.

 Workshop Co-Chair: Zoe Paraskevopoulou      (Northeastern University)
 Workshop Co-Chair: Leonidas Lampropoulos     (University of Maryland)
 General Chair:     Sukyoung Ryu                               (KAIST)
 Program Chair:     Ronald Garcia     (University of British Columbia)


----------------------------------------------------------------------

Further information

Any queries should be addressed to the workshop co-chairs (Zoe 
Paraskevopoulou and Leonidas Lampropoulos), via email to
icfp-workshops-2021 at googlegroups.com.


From delphine.demange at irisa.fr  Sun Nov  8 18:33:44 2020
From: delphine.demange at irisa.fr (Delphine Demange)
Date: Sun, 8 Nov 2020 19:33:44 +0100
Subject: [Haskell-cafe] Extended Deadline - Compiler Construction (CC) 2021
Message-ID: <1AE9BBE6-EDF4-4B3B-992A-872C0B05D9D1@irisa.fr>

ACM SIGPLAN 2021 International Conference on Compiler Construction (CC 2021)
Co-located with CGO, HPCA and PPoPP
Tue 2 - Wed 3 March 2021
https://conf.researchr.org/home/CC-2021

CALL FOR PAPERS

The International Conference on Compiler Construction (CC) is
interested in work on processing programs in the most general sense:
analyzing, transforming or executing input that describes how a system
operates, including traditional compiler construction as a special
case.

The abstract and full paper submission is now November 13, 2020.

= IMPORTANT DATES = 
Abstract & Full Paper Submission: November 13, 2020 (EXTENDED)
Author Response Period: December 7 - 9, 2020 
Author Notification: December 22, 2020
Artifact Submission: January 5, 2021
AE Notification: January 20, 2021
Final Papers due: January 22, 2021
Conference: March 2 - 3, 2021

Original contributions are solicited on the topics of interest which
include, but are not limited to:

- Compilation and interpretation techniques, including program
  representation, analysis, and transformation; code generation,
  optimization, and synthesis; the verification thereof
- Run-time techniques, including memory management, virtual machines,
  and dynamic and just-in-time compilation
- Programming tools, including refactoring editors, checkers,
  verifiers, compilers, debuggers, and profilers
- Techniques, ranging from programming languages to
  micro-architectural support, for specific domains such as secure,
  parallel, distributed, embedded or mobile environments
- Design and implementation of novel language constructs, programming
  models, and domain-specific languages

CC is an ACM SIGPLAN conference, and implements guidelines and
procedures recommended by SIGPLAN (https://www.sigplan.org).

Prospective authors should be aware of SIGPLAN’s Copyright
policies. Proceedings will be made available online in the ACM digital
library from one week before to one week after the conference.

Full CfP: https://conf.researchr.org/track/CC-2021/cc-research-papers

ARTIFACT EVALUATION

Authors of accepted papers will be invited to submit their artifacts
for the Artifact Evaluation (AE). The Artifact Evaluation process
begins after the acceptance notification, and is run by a separate
committee whose task is to assess how the artifacts support the work
described in the papers.

To ease the organization of the AE committee, we kindly ask authors to
indicate at the time they submit the paper, whether they are
interested in submitting an artifact.

Papers that go through the Artifact Evaluation process successfully
will receive a seal of approval printed on the papers themselves.

Authors of accepted papers are encouraged, but not required, to make
these materials publicly available upon publication of the
proceedings, by including them as “source materials” in the ACM
Digital Library.

CC AE web page:
https://conf.researchr.org/track/CC-2021/research-artifacts

ORGANIZERS

General Chair:
    Aaron Smith - Microsoft / University of Edinburgh

Program Chairs: 
    Delphine Demange - Univ Rennes, Inria, CNRS, IRISA
    Rajiv Gupta - UC Riverside

Artifact Evaluation Chairs:
    Bruno Bodin - Yale-NUS College
    Michel Steuwer - University of Glasgow

Web Chair:
    Martin Lücke - University of Edinburgh

Steering Committee:
    Björn Franke (Chair) - University of Edinburgh
    Jose Nelson Amaral - University of Alberta
    Christophe Dubach - University of Edinburgh
    Sebastian Hack - Saarland University
    Manuel Hermenegildo - IMDEA Software Institute and T.U. of Madrid (UPM)
    Alexandra Jimborean - University of Murcia
    Milind Kulkarni - Purdue University
    Louis-Noël Pouchet - Colorado State University
    Peng Wu - Futurewei Technologies
    Jingling Xue - UNSW Sydney
    Ayal Zaks - Intel Corporation and Technion

Program Committee:
    Guillaume Baudart - IBM Research
    Walter Binder - University of Lugano
    Simone Campanoni - Northwestern University
    Albert Cohen - Google
    Caroline Collange - Inria, Univ Rennes, CNRS, IRISA
    Huimin Cui - Institute of Computing Technology, CAS
    Christophe Dubach - McGill University
    Benoît Dupont de Dinechin - Kalray
    Bernhard Egger - Seoul National University
    Christine Flood - Red Hat
    Laure Gonnord - University of Lyon and LIP
    Myoungsoo Jung - KAIST
    Andrew Kennedy - Facebook
    Dongyoon Lee - Stony Brook University
    Christian Lengauer - University of Passau
    Xavier Leroy - Collège de France and Inria
    Yun Liang - Peking University
    Toby Murray - University of Melbourne and Data61
    Biswabandan Panda - Indian Institute of Technology Kanpur
    Santosh Pande - Georgia Tech
    Louis-Noël Pouchet - Colorado State University
    Gabriel Rodríguez - Universidade da Coruña
    Jan Vitek - Northeastern University
    Jingling Xue - UNSW Sydney
    Zhijia Zhao - UC Riverside


From stefan.wehr at gmail.com  Tue Nov 10 08:54:44 2020
From: stefan.wehr at gmail.com (Stefan Wehr)
Date: Tue, 10 Nov 2020 09:54:44 +0100
Subject: [Haskell-cafe] Last Call for Contributions: BOB 2021 [Feb 26,
	Deadline Nov 13]
Message-ID: <CAJAdMdH0=jd67PDS6L9fpDS2PyaZ68pUc3q0GL5QMu837E1R2Q@mail.gmail.com>

  BOB Conference 2021

         "What happens when we use what's best for a change?"
                  http://bobkonf.de/2021/cfc.html
                         Berlin, February 26
                        Call for Contributions
                     Deadline: November 13, 2020

You are actively engaged in advanced software engineering methods,
implement ambitious architectures and are open to cutting-edge
innovation? Attend this conference, meet people that share your goals,
and get to know the best software tools and technologies available
today. We strive to offer a day full of new experiences and
impressions that you can use to immediately improve your daily life as
a software developer.

If you share our vision and want to contribute, submit a proposal for
a talk or tutorial!

NOTE: The conference fee will be waived for presenters. Travel
expenses will not be covered (for exceptions see "Speaker Grants").
Online or Onsite

We do know yet whether BOB will happen onsite in Berlin or as an
online event. Should BOB happen online, we will likely ask for
pre-recorded talks to make room for questions and social interactions
during the actual conference day. (Of course, we'll provide assistance
making those recordings.) Tutorials will likely happen as a
live-session.

Speaker Grants
--------------

BOB has Speaker Grants available to support speakers from groups
under-represented in technology. We specifically seek women speakers,
speakers of color, and speakers who are not be able to attend the
conference for financial reasons.

Shepherding
-----------

The program committee offers shepherding to all speakers. Shepherding
provides speakers assistance with preparing their
sessions. Specifically:

- advice on structure and presentation
- review of talk slides
- assistance with recording
- review of recording, if applicable

Topics
------

We are looking for talks about best-of-breed software technology,
e.g.:

- functional programming
- persistent data structures and databases
- event-based modelling and architecture
- types
- formal methods for correctness and robustness
- abstractions for concurrency and parallelism
- metaprogramming
- probabilistic programming
- math and programming
- controlled side effects
- beyond REST and SOAP
- effective abstractions for data analytics
- … everything really that isn’t mainstream, but you think should be.

Presenters should provide the audience with information that is
practically useful for software developers.

We're especially interested in experience reports.  Other topics are
also relevant, e.g.:

- introductory talks on technical background
- overviews of a given field
- demos and how-tos

Requirements
------------

We accept proposals for presentations of 45 minutes (40 minutes talk +
5 minutes questions), as well as 90 minute tutorials for
beginners. The language of presentation should be either English or
German.

Your proposal should include (in your presentation language of choice):

- An abstract of max. 1500 characters.
- A short bio/cv
- Contact information (including at least email address)
- A list of 3-5 concrete ideas of how your work can be applied in a
developer's daily life
- additional material (websites, blogs, slides, videos of past presentations, …)
- Don't be confused: The system calls a submission event.

Organisation
------------

- Direct questions to contact at bobkonf dot de
- Proposal deadline: November 13, 2020
- Notification: November 27, 2020
- Program: December 6, 2020

Submit here:
https://bobcfc.active-group.de/en/bob2021/cfp

Program Committee
-----------------

(more information here: https://bobkonf.de/2020/programmkomitee.html)

- Matthias Fischmann, Wire
- Matthias Neubauer, SICK AG
- Nicole Rauch, Softwareentwicklung und Entwicklungscoaching
- Michael Sperber, Active Group
- Stefan Wehr, Hochschule Offenburg

Scientific Advisory Board

- Annette Bieniusa, TU Kaiserslautern
- Torsten Grust, Uni Tübingen
- Peter Thiemann, Uni Freiburg
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From ky3 at atamo.com  Tue Nov 10 23:23:01 2020
From: ky3 at atamo.com (Kim-Ee Yeoh)
Date: Wed, 11 Nov 2020 06:23:01 +0700
Subject: [Haskell-cafe] What to call Occult Effects
Message-ID: <CAPY+ZdTzQr0XVQvrt=GeyO0w+ynqc0RwMByK3k=ayghb3Ej03w@mail.gmail.com>

By an occult effect I mean that under the type signature (M a -> M b -> M
b) of a particular monad M, the two expressions (const id) and (liftM2 $
const id) are equivalent.

Occult here refers to how the effect of the second parameter blocks the
effect of the first one.

In your opinion, is there a better word than occult to describe the
property of such monads?
-- 
-- Kim-Ee
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From mgajda at mimuw.edu.pl  Wed Nov 11 13:36:29 2020
From: mgajda at mimuw.edu.pl (Michal J Gajda)
Date: Wed, 11 Nov 2020 14:36:29 +0100
Subject: [Haskell-cafe] Occult effects...
In-Reply-To: <CAPY+ZdTQXVL6HuFzZGDZX975Orvr68CzVgpK8rfSjfMDsrNGMg@mail.gmail.com>
References: <CACQVYRCfpf6uk0NTDN+ihBtfHuEkZHoypQ73Vt8C+HNnEf678Q@mail.gmail.com>
 <CAPY+ZdTQXVL6HuFzZGDZX975Orvr68CzVgpK8rfSjfMDsrNGMg@mail.gmail.com>
Message-ID: <CACQVYRAP7YthGuf4-r7e8CfOqbakzU71N3fNQesXo94AMb3ROw@mail.gmail.com>

It is easier to understand it if:
1. You give some examples of such monads
2. Describe how this property arises
3. Tell how whether the law is unique or part of a list of laws applicable

Most of mathematics we do is not entirely disconnected from applications.

If I tell you there is a class of monoids `m` over a set of objects `o` :

class Monoid m => T m o where
  i :: o -> t
  c :: t -> o -> Bool

Such that the following laws are satisfied:

Forall x y z m n.
c (i x) x =True
c mempty x = False
c m y = True => c (m <> n) y = True
c n y = True => c (m <> n) y = True

What does it tell you about the definitions?
Can you tell if this set of laws is correctly stated or exhaustive?
Whether it models what I intend to do?
Without further examples could I claim that it may be universal model for
some phenomena f and g?

Or would you rather see some examples or descriptions of i and c operations?


PS you may respond to haskell-cafe, sure. I did not think that my previous
question deserved sharing, but this answer certainly does.
--
  Cheers
     Michał

On Wed, Nov 11, 2020, 14:04 Kim-Ee Yeoh <ky3 at atamo.com> wrote:

> Hi Michal,
>
> How is it hermetic? I think I fully described the property whose name I am
> opening to discussion.
>
> What is lacking in the definition?
>
> Also, do you mind having this discussion at the cafe itself? You are
> probably not the only one with this query.
>
> On Wed, Nov 11, 2020 at 7:37 PM Michał J Gajda <mjgajda at gmail.com> wrote:
>
>> Hi,
>> Your post to haskell-cafe is somewhat hermetic if you do not provide
>> additional examples.
>> What do you use these for?
>> --
>>   Cheers
>>     Michał
>>
> --
> -- Kim-Ee
>
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From Graham.Hutton at nottingham.ac.uk  Wed Nov 11 15:49:42 2020
From: Graham.Hutton at nottingham.ac.uk (Graham Hutton)
Date: Wed, 11 Nov 2020 15:49:42 +0000
Subject: [Haskell-cafe] Three new Teaching Assistant positions in Nottingham
Message-ID: <6EE5E75F-ED15-4993-BB25-AAEAC551BFA0@nottingham.ac.uk>

Dear all,

As part of a strategic expansion, the School of Computer Science
at the University of Nottingham is seeking to make three new
permanent appointments at Teaching Assistant level:

   https://www.nottingham.ac.uk/jobs/currentvacancies/ref/SCI290020

Applicants with expertise in functional programming are strongly
encouraged!  The deadline for applications is 11th December 2020.

Best wishes,

Graham

—
Professor Graham Hutton
School of Computer Science
University of Nottingham, UK
http://www.cs.nott.ac.uk/~pszgmh






This message and any attachment are intended solely for the addressee
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From olf at aatal-apotheke.de  Wed Nov 11 22:35:18 2020
From: olf at aatal-apotheke.de (Olaf Klinke)
Date: Wed, 11 Nov 2020 23:35:18 +0100
Subject: [Haskell-cafe] What to call Occult Effects (Kim-Ee Yeoh)
Message-ID: <88b8803d8dc778bf008e051876beb3dba582d1e1.camel@aatal-apotheke.de>

> By an occult effect I mean that under the type signature (M a -> M b
> -> M
> b) of a particular monad M, the two expressions (const id) and
> (liftM2 $
> const id) are equivalent.
> 
> Occult here refers to how the effect of the second parameter blocks
> the
> effect of the first one.
> 
> In your opinion, is there a better word than occult to describe the
> property of such monads?

Dear Kim-Ee,

TL;DR: Why not the simpler  
	do {y <- b; a} = a

My name for your property would be "distribution-like" or "lazy"
because of an old post of mine [1]. In that thread we discussed models
of probability and I emphasized the property 

fmap.const = const.return :: a -> M b -> M a    (Functor-const)

which we will see is equivalent to your occultness. Categorically it
can be re-phrased as: "M as a functor maps constant functions to
constant functions."

First, instead of `const id` I will use `const`, that is, we shall
prove 

const = liftM2 const :: M a -> M b -> M a       (occultness)

which I believe should be equivalent to your property. For the proof it
will be convenient to use the following. 

Lemma: liftM2 f a b = a >>= (\x -> fmap (f x) b)
Proof: We de-sugar the do-notation in the source code for liftM2. 

liftM2 f a b = a >>= (\x -> b >>= (\y -> return (f x y)))

Now use the equation fmap h b = b >>= (\y -> return (h y)) with h
instantiated to `f x` to obtain the desired identity. q.e.d. 
Armed with the Lemma we instantiate f = const.

liftM2 const a b = a >>= (\x -> fmap (const x) b)

If we now assume my property (Functor-const) then we may re-write  to 

liftM2 const a b = a >>= (\x -> const (return x) b)
                 = a >>= (\x -> return x)
                 = a

We have shown (Functor-const) implies (occultness). 
For the reverse implication, we shall prove (Functor-const) holds with
the arguments swapped, that is, we prove the equation

\b -> \x -> fmap (const x) b = \b -> \x -> return x

Starting with the left-hand side, we eta-expand using the law 
(k :: a -> M b) x = return x >>= k
and obtain 

\b -> \x -> (return x >>= (\x -> fmap (const x) b))

Using the Lemma we identify the expression in the outermost parentheses
as liftM2 const (return x) b which by assumption equals return x,
whence we re-write the entire term to

\b -> \x -> return x

q.e.d. 

Next consider a law with the same type as (occultness):

(=<<).const = const :: M a -> M b -> M a      (Kleisli-const)
do {y <- b; a} = a                         (same in do-notation)

Any MonadPlus fails this due to the law 
k =<< mzero = mzero. Categorically it can be re-phrased as 
"The functor from the Kleisli category of M to Hask preserves constant
arrows."
I will prove that if M is commutative then (Kleisli-const) implies
(occultness). 

liftM2 const a b 
= do {x <- a; y <- b; return (const x y)}
= do {y <- b; x <- a; return (const x y)}  (by commutative)
= do {y <- b; x <- a; return x}
= do {y <- b; a}
= a                                        (by Kleisli-const)

Probability distributions have property (Functor-const) because it
essentially says that if you map any distribution through a constant
function, you will end up with all mass in one place. It is related to
lazyness because a priori 

const a :: M b -> M a

is lazy in its argument whereas 

\b -> a >>= (\x -> fmap (const x) b) 

is not lazy a priori, i.e. may examine its argument b and execute side-
effects. Such lazyness was desired in [1] because inspecting an
argument in that context meant computationally expensive sampling of a
random distribution. 

Are there concrete Haskell monads with this property? 
NonEmpty lists have this property up to multiplicity and order, that
is, non-empty finite sets are an example of an occult M. 
The Reader monad is easily seen to have this property. And that seems
to be all. 
Observe that my two example monads above are indeed commutative and
have the property (Kleisli-const). I'm curious whether (Kleisli-const)
makes sense in your application. 

Olaf


[1] 
https://mail.haskell.org/pipermail/haskell-cafe/2019-October/131605.html


From ky3 at atamo.com  Thu Nov 12 01:33:34 2020
From: ky3 at atamo.com (Kim-Ee Yeoh)
Date: Thu, 12 Nov 2020 08:33:34 +0700
Subject: [Haskell-cafe] What to call Occult Effects
In-Reply-To: <CAPY+ZdTzQr0XVQvrt=GeyO0w+ynqc0RwMByK3k=ayghb3Ej03w@mail.gmail.com>
References: <CAPY+ZdTzQr0XVQvrt=GeyO0w+ynqc0RwMByK3k=ayghb3Ej03w@mail.gmail.com>
Message-ID: <CAPY+ZdQ=4QcH2J0HfPfx+31+_4BvkQ3R5o_xX5=V5ud6Q7FpnA@mail.gmail.com>

(I'll respond with the original subject heading and with the full thread of
Michal's reply copied below so that the convo stays in one place.)

Hi Michal, I'm afraid you caricaturize my original email out of proportion
here:

> class Monoid m => T m o where
> i :: o -> t
> c :: t -> o -> Bool
<snip>

Not only is your T type class more complicated than what I wrote, it's also
riddled with suggestive but possibly misleading one-letter variable names.
You even ask your reader to stay wary of the laws (snipped) that might not
even be correctly stated.

I do no such thing in my original email.

In fact, the modicum of Haskell background that suffices for grasping the
original query is only the next level up from recognizing that a
universally polymorphic function of type (a -> a -> a) is inhabited by
exactly two functions, modulo bottom.

>From there it's one more step to how (forall m. Monad m => m a -> m b -> m
b) is inhabited by a mere handful of functions, again barring bottom. My
query makes reference to how two of the those functions, namely (const id)
and (liftM2 $ const id) are equivalent with some monads but not others.

I even gave further clarification in plain English about "how the effect of
the second parameter blocks the effect of the first."

At the top of your email you wrote:

> It is easier to understand it if:
> 1. You give some examples of such monads
> 2. Describe how this property arises
> 3. Tell how whether the law is unique or part of a list of laws applicable

Are you alluding to the X-Y problem?

http://xyproblem.info/

I assure you I labor under no such tunnel-vision.

Were I to request a cromulent adjective for the seventh powers of the
natural numbers, what progress do you make by making counter-demands for
examples?

Behind which string of digits does the pellucid word hide itself?

-- Kim-Ee

On Wed, Nov 11, 2020 at 8:36 PM Michal J Gajda <mgajda at mimuw.edu.pl> wrote:

> It is easier to understand it if:
> 1. You give some examples of such monads
> 2. Describe how this property arises
> 3. Tell how whether the law is unique or part of a list of laws applicable
>
> Most of mathematics we do is not entirely disconnected from applications.
>
> If I tell you there is a class of monoids `m` over a set of objects `o` :
>
> class Monoid m => T m o where
>   i :: o -> t
>   c :: t -> o -> Bool
>
> Such that the following laws are satisfied:
>
> Forall x y z m n.
> c (i x) x =True
> c mempty x = False
> c m y = True => c (m <> n) y = True
> c n y = True => c (m <> n) y = True
>
> What does it tell you about the definitions?
> Can you tell if this set of laws is correctly stated or exhaustive?
> Whether it models what I intend to do?
> Without further examples could I claim that it may be universal model for
> some phenomena f and g?
>
> Or would you rather see some examples or descriptions of i and c
> operations?
>
>
> PS you may respond to haskell-cafe, sure. I did not think that my previous
> question deserved sharing, but this answer certainly does.
> --
>   Cheers
>      Michał
>
> On Wed, Nov 11, 2020, 14:04 Kim-Ee Yeoh <ky3 at atamo.com> wrote:
>
>> Hi Michal,
>>
>> How is it hermetic? I think I fully described the property whose name I
>> am opening to discussion.
>>
>> What is lacking in the definition?
>>
>> Also, do you mind having this discussion at the cafe itself? You are
>> probably not the only one with this query.
>>
>> On Wed, Nov 11, 2020 at 7:37 PM Michał J Gajda <mjgajda at gmail.com> wrote:
>>
>>> Hi,
>>> Your post to haskell-cafe is somewhat hermetic if you do not provide
>>> additional examples.
>>> What do you use these for?
>>> --
>>>   Cheers
>>>     Michał
>>>
>> --
>> -- Kim-Ee
>>
> --
-- Kim-Ee
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From msm at gwmail.gwu.edu  Thu Nov 12 01:38:17 2020
From: msm at gwmail.gwu.edu (Michael Matsko)
Date: Thu, 12 Nov 2020 01:38:17 +0000
Subject: [Haskell-cafe] What to call Occult Effects
In-Reply-To: <CAPY+ZdQ=4QcH2J0HfPfx+31+_4BvkQ3R5o_xX5=V5ud6Q7FpnA@mail.gmail.com>
References: <CAPY+ZdTzQr0XVQvrt=GeyO0w+ynqc0RwMByK3k=ayghb3Ej03w@mail.gmail.com>,
 <CAPY+ZdQ=4QcH2J0HfPfx+31+_4BvkQ3R5o_xX5=V5ud6Q7FpnA@mail.gmail.com>
Message-ID: <BN3PR0801MB2273855BA1CD0220C046DCD8A8E70@BN3PR0801MB2273.namprd08.prod.outlook.com>

Also, I think you want to say occlude, which means block from view, as opposed to occult which refers to magic and such.  Which may, or may not be what you want.

Mike

Michael Matsko
________________________________
From: Haskell-Cafe <haskell-cafe-bounces at haskell.org> on behalf of Kim-Ee Yeoh <ky3 at atamo.com>
Sent: Wednesday, November 11, 2020 8:33:34 PM
To: Haskell Cafe <haskell-cafe at haskell.org>; mgajda at mimuw.edu.pl <mgajda at mimuw.edu.pl>
Subject: Re: [Haskell-cafe] What to call Occult Effects

(I'll respond with the original subject heading and with the full thread of Michal's reply copied below so that the convo stays in one place.)

Hi Michal, I'm afraid you caricaturize my original email out of proportion here:

> class Monoid m => T m o where
> i :: o -> t
> c :: t -> o -> Bool
<snip>

Not only is your T type class more complicated than what I wrote, it's also riddled with suggestive but possibly misleading one-letter variable names. You even ask your reader to stay wary of the laws (snipped) that might not even be correctly stated.

I do no such thing in my original email.

In fact, the modicum of Haskell background that suffices for grasping the original query is only the next level up from recognizing that a universally polymorphic function of type (a -> a -> a) is inhabited by exactly two functions, modulo bottom.

>From there it's one more step to how (forall m. Monad m => m a -> m b -> m b) is inhabited by a mere handful of functions, again barring bottom. My query makes reference to how two of the those functions, namely (const id) and (liftM2 $ const id) are equivalent with some monads but not others.

I even gave further clarification in plain English about "how the effect of the second parameter blocks the effect of the first."

At the top of your email you wrote:

> It is easier to understand it if:
> 1. You give some examples of such monads
> 2. Describe how this property arises
> 3. Tell how whether the law is unique or part of a list of laws applicable

Are you alluding to the X-Y problem?

http://xyproblem.info/

I assure you I labor under no such tunnel-vision.

Were I to request a cromulent adjective for the seventh powers of the natural numbers, what progress do you make by making counter-demands for examples?

Behind which string of digits does the pellucid word hide itself?

-- Kim-Ee

On Wed, Nov 11, 2020 at 8:36 PM Michal J Gajda <mgajda at mimuw.edu.pl<mailto:mgajda at mimuw.edu.pl>> wrote:
It is easier to understand it if:
1. You give some examples of such monads
2. Describe how this property arises
3. Tell how whether the law is unique or part of a list of laws applicable

Most of mathematics we do is not entirely disconnected from applications.

If I tell you there is a class of monoids `m` over a set of objects `o` :

class Monoid m => T m o where
  i :: o -> t
  c :: t -> o -> Bool

Such that the following laws are satisfied:

Forall x y z m n.
c (i x) x =True
c mempty x = False
c m y = True => c (m <> n) y = True
c n y = True => c (m <> n) y = True

What does it tell you about the definitions?
Can you tell if this set of laws is correctly stated or exhaustive?
Whether it models what I intend to do?
Without further examples could I claim that it may be universal model for some phenomena f and g?

Or would you rather see some examples or descriptions of i and c operations?


PS you may respond to haskell-cafe, sure. I did not think that my previous question deserved sharing, but this answer certainly does.
--
  Cheers
     Michał

On Wed, Nov 11, 2020, 14:04 Kim-Ee Yeoh <ky3 at atamo.com<mailto:ky3 at atamo.com>> wrote:
Hi Michal,

How is it hermetic? I think I fully described the property whose name I am opening to discussion.

What is lacking in the definition?

Also, do you mind having this discussion at the cafe itself? You are probably not the only one with this query.

On Wed, Nov 11, 2020 at 7:37 PM Michał J Gajda <mjgajda at gmail.com<mailto:mjgajda at gmail.com>> wrote:
Hi,
Your post to haskell-cafe is somewhat hermetic if you do not provide additional examples.
What do you use these for?
--
  Cheers
    Michał
--
-- Kim-Ee
--
-- Kim-Ee
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From ky3 at atamo.com  Thu Nov 12 01:42:26 2020
From: ky3 at atamo.com (Kim-Ee Yeoh)
Date: Thu, 12 Nov 2020 08:42:26 +0700
Subject: [Haskell-cafe] What to call Occult Effects
In-Reply-To: <CABPxb2nONNs=0GmJiKEb3Ju3zJ-xJ5Wks_h=hF3NbH6J_ZwWKg@mail.gmail.com>
References: <CAPY+ZdTzQr0XVQvrt=GeyO0w+ynqc0RwMByK3k=ayghb3Ej03w@mail.gmail.com>
 <CABPxb2nONNs=0GmJiKEb3Ju3zJ-xJ5Wks_h=hF3NbH6J_ZwWKg@mail.gmail.com>
Message-ID: <CAPY+ZdS+T04Ef-x=X46aWyXmnuyAoa2h2kp+omm3ggTRrtcanw@mail.gmail.com>

On Thu, Nov 12, 2020 at 12:17 AM Justin Bailey <jgbailey at gmail.com> wrote:

> Looking up the definition "occult" on duckduckgo
> (https://duckduckgo.com/?t=ffab&q=occult+definition&ia=definition)
> gives this response:
>
>   adj. Of, relating to, or dealing with supernatural or magical
> influences, agencies, or occurrences.
>   adj. Available only to the initiate; secret or mysterious: synonym:
> mysterious.
>   adj. Beyond the realm of human comprehension; inscrutable.
>
> Doesn't seem to really apply to your type signature. If you mean in
> the sense of "occlusion" or "occludes", I'd be specific ("occluded
> effects").


Hi Justin,

Thank you for heads up, it's just the nudge I need that "occult" probably
isn't the right word although I had the astronomical usage in mind.

My go-to solution is now "occlusive effects" unless something even better
comes along.


>
> On Tue, Nov 10, 2020 at 3:24 PM Kim-Ee Yeoh <ky3 at atamo.com> wrote:
> >
> > By an occult effect I mean that under the type signature (M a -> M b ->
> M b) of a particular monad M, the two expressions (const id) and (liftM2 $
> const id) are equivalent.
> >
> > Occult here refers to how the effect of the second parameter blocks the
> effect of the first one.
> >
> > In your opinion, is there a better word than occult to describe the
> property of such monads?
> > --
> > -- Kim-Ee
> > _______________________________________________
> > Haskell-Cafe mailing list
> > To (un)subscribe, modify options or view archives go to:
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> > Only members subscribed via the mailman list are allowed to post.
>
-- 
-- Kim-Ee
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From david.feuer at gmail.com  Thu Nov 12 02:47:43 2020
From: david.feuer at gmail.com (David Feuer)
Date: Wed, 11 Nov 2020 21:47:43 -0500
Subject: [Haskell-cafe] What to call Occult Effects
In-Reply-To: <CAPY+ZdTzQr0XVQvrt=GeyO0w+ynqc0RwMByK3k=ayghb3Ej03w@mail.gmail.com>
References: <CAPY+ZdTzQr0XVQvrt=GeyO0w+ynqc0RwMByK3k=ayghb3Ej03w@mail.gmail.com>
Message-ID: <CAMgWh9v5aWp=TW=jpgzjrfphtMNYAmoNpP8qnextgj-xj+MDaw@mail.gmail.com>

Interesting. There seem to be quite a few of these.

const id (Identity x) (Identity y) = Identity y = liftA2 (const id)
(Identity x) (Identity y)

If m is occlusive, so is ReaderT e m:

liftA2 (const id) (ReaderT f) (ReaderT g) = ReaderT $ \r -> liftA2 (const
id) (f r) (g r) = ReaderT $ \r -> g r = ReaderT g

I believe this works for StateT as well. The first counterexample is Writer
w for a non-trivial monoid w.

On Tue, Nov 10, 2020, 6:23 PM Kim-Ee Yeoh <ky3 at atamo.com> wrote:

> By an occult effect I mean that under the type signature (M a -> M b -> M
> b) of a particular monad M, the two expressions (const id) and (liftM2 $
> const id) are equivalent.
>
> Occult here refers to how the effect of the second parameter blocks the
> effect of the first one.
>
> In your opinion, is there a better word than occult to describe the
> property of such monads?
> --
> -- Kim-Ee
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From ietf-dane at dukhovni.org  Thu Nov 12 04:57:15 2020
From: ietf-dane at dukhovni.org (Viktor Dukhovni)
Date: Wed, 11 Nov 2020 23:57:15 -0500
Subject: [Haskell-cafe] What to call Occult Effects
In-Reply-To: <CAMgWh9v5aWp=TW=jpgzjrfphtMNYAmoNpP8qnextgj-xj+MDaw@mail.gmail.com>
References: <CAPY+ZdTzQr0XVQvrt=GeyO0w+ynqc0RwMByK3k=ayghb3Ej03w@mail.gmail.com>
 <CAMgWh9v5aWp=TW=jpgzjrfphtMNYAmoNpP8qnextgj-xj+MDaw@mail.gmail.com>
Message-ID: <20201112045715.GK1464@straasha.imrryr.org>

On Wed, Nov 11, 2020 at 09:47:43PM -0500, David Feuer wrote:

> If m is occlusive, so is ReaderT e m:
> 
> [...]
> 
> I believe this works for StateT as well.

I am puzzled what you mean by that, given that

    State s a = StateT s Identity a

and while "Identity" is "occlusive", State is not.

    λ> import Control.Monad
    λ> import Control.Monad.Trans.State.Strict
    λ> runState (liftM2 (const id) (put True :: State Bool ()) get) False
    (True,True)
    λ> runState ((const id) (put True :: State Bool ()) get) False
    (False,False)

-- 
    Viktor.

From david.feuer at gmail.com  Thu Nov 12 04:59:12 2020
From: david.feuer at gmail.com (David Feuer)
Date: Wed, 11 Nov 2020 23:59:12 -0500
Subject: [Haskell-cafe] What to call Occult Effects
In-Reply-To: <20201112045715.GK1464@straasha.imrryr.org>
References: <CAPY+ZdTzQr0XVQvrt=GeyO0w+ynqc0RwMByK3k=ayghb3Ej03w@mail.gmail.com>
 <CAMgWh9v5aWp=TW=jpgzjrfphtMNYAmoNpP8qnextgj-xj+MDaw@mail.gmail.com>
 <20201112045715.GK1464@straasha.imrryr.org>
Message-ID: <CAMgWh9sRNOUNZivm+LdhH=Sh2qKEKwmaGY5FTwXew++sQJb18w@mail.gmail.com>

Ah, you're right. I wrote that while recovering from a migraine, and it was
bogus!

On Wed, Nov 11, 2020, 11:57 PM Viktor Dukhovni <ietf-dane at dukhovni.org>
wrote:

> On Wed, Nov 11, 2020 at 09:47:43PM -0500, David Feuer wrote:
>
> > If m is occlusive, so is ReaderT e m:
> >
> > [...]
> >
> > I believe this works for StateT as well.
>
> I am puzzled what you mean by that, given that
>
>     State s a = StateT s Identity a
>
> and while "Identity" is "occlusive", State is not.
>
>     λ> import Control.Monad
>     λ> import Control.Monad.Trans.State.Strict
>     λ> runState (liftM2 (const id) (put True :: State Bool ()) get) False
>     (True,True)
>     λ> runState ((const id) (put True :: State Bool ()) get) False
>     (False,False)
>
> --
>     Viktor.
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From mgajda at mimuw.edu.pl  Thu Nov 12 13:30:15 2020
From: mgajda at mimuw.edu.pl (Michal J Gajda)
Date: Thu, 12 Nov 2020 14:30:15 +0100
Subject: [Haskell-cafe] What to call Occult Effects
In-Reply-To: <CAPY+ZdQ=4QcH2J0HfPfx+31+_4BvkQ3R5o_xX5=V5ud6Q7FpnA@mail.gmail.com>
References: <CAPY+ZdTzQr0XVQvrt=GeyO0w+ynqc0RwMByK3k=ayghb3Ej03w@mail.gmail.com>
 <CAPY+ZdQ=4QcH2J0HfPfx+31+_4BvkQ3R5o_xX5=V5ud6Q7FpnA@mail.gmail.com>
Message-ID: <CACQVYRCEEje3De3_xkLbTVhtVXTJxrM9GA6M6gEmOwWTWWuxtg@mail.gmail.com>

Dear Kim,

This was not intended as caricature at all. But it seems an excellent
example of x-y problem indeed.
When asking for a real life examples, I provided a case when I can
provide example that is familiar to most readers:

T = Types
i = infer :: object -> type
c = check :: type -> object -> Bool

Laws just make sure that type checking is preserved over unification
or anti-unification (<>),
except for commutativity - which is omitted on purpose (further
description here: https://arxiv.org/abs/2011.03076.)

Naturally this example just enumerates the laws that are true for both
unification and anti-unification problems.

Your question would be however fitting for ICFP 2021 trivia, since
without examples provided by other haskell-cafe readers
I would not have guessed that you want to mean "occlusion", instead of
magic of "occult" here.

On Thu, Nov 12, 2020 at 2:33 AM Kim-Ee Yeoh <ky3 at atamo.com> wrote:
>
> (I'll respond with the original subject heading and with the full thread of Michal's reply copied below so that the convo stays in one place.)
>
> Hi Michal, I'm afraid you caricaturize my original email out of proportion here:
>
> > class Monoid m => T m o where
> > i :: o -> t
> > c :: t -> o -> Bool
> <snip>
(...)
> On Wed, Nov 11, 2020 at 8:36 PM Michal J Gajda <mgajda at mimuw.edu.pl> wrote:
(...)
>> Such that the following laws are satisfied:
>>
>> Forall x y z m n.
>> c (i x) x =True
>> c mempty x = False
>> c m y = True => c (m <> n) y = True
>> c n y = True => c (m <> n) y = True
>>
>> What does it tell you about the definitions?
>> Can you tell if this set of laws is correctly stated or exhaustive?
>> Whether it models what I intend to do?
>> Without further examples could I claim that it may be universal model for some phenomena f and g?
-- 
  Cheers
    Michał

From olf at aatal-apotheke.de  Thu Nov 12 20:58:51 2020
From: olf at aatal-apotheke.de (Olaf Klinke)
Date: Thu, 12 Nov 2020 21:58:51 +0100
Subject: [Haskell-cafe] What to call Occult Effects
Message-ID: <8089bc77dacb56f80d05e10a1ce43f37d074b613.camel@aatal-apotheke.de>

> First, instead of `const id` I will use `const`, that is, we shall
> prove 
> 
> const = liftM2 const :: M a -> M b -> M a
> 
> which I believe should be equivalent to your property.

My belief was wrong, which is evident when using do-notation. 
Kim-Ee stated

do {_ <- b; x <- a; return x} = a

while I examined 

do {x <- a; _ <- b; return x} = a

Since do {x <- a; return x} = a holds for any monad, Kim-Ee's property
can be reduced to 

do {_ <- b; a} = a
or more concisely 
b >> a = a

which I called Kleisli-const in my previous post. As we seemed to have
settled for "occlusive" I suggest calling 
b >> a = a
"right-occlusive" or "occlusive from the right" because the right
action occludes the side-effects of the left action, and 
do {x <- a; _ <- b; return x} = a
should be called "left-occlusive" or "occlusive from the left" because
the left action hides the effect of the right action. Under
commutativity, both are the same but in general these might be
different properties. I do not have a distinguishing counterexample,
though, because all monads I come up with are commutative. 

David Feuer hinted at the possibility to define occlusiveness more
generally for Applicative functors. Commutativity might be stated for
Applicatives as 

liftA2 f a b = liftA2 (flip f) b a

So far I can only see two classes of occlusive monads: The reader-like
(Identity ~ Reader ()) and the set-like monads. 

Olaf


From david.feuer at gmail.com  Thu Nov 12 21:25:53 2020
From: david.feuer at gmail.com (David Feuer)
Date: Thu, 12 Nov 2020 16:25:53 -0500
Subject: [Haskell-cafe] What to call Occult Effects
In-Reply-To: <8089bc77dacb56f80d05e10a1ce43f37d074b613.camel@aatal-apotheke.de>
References: <8089bc77dacb56f80d05e10a1ce43f37d074b613.camel@aatal-apotheke.de>
Message-ID: <CAMgWh9to1TUvEQ=ivfO9areF25Hd+BCvJxWYyQbNTW5k3MQRxw@mail.gmail.com>

First, for clarity, note that

   const id = flip const

Consider a (right-)occlusive functor. We immediately see that

liftA2 (flip const) m (pure x) = pure x

Using the Applicative laws, we can restate this:

x <$ m = pure x

We get the same sort of result for a left-occlusive effect.

So an occlusive effect can't have any *observable* side effects. It must be
"read only".

On Thu, Nov 12, 2020, 3:59 PM Olaf Klinke <olf at aatal-apotheke.de> wrote:

> > First, instead of `const id` I will use `const`, that is, we shall
> > prove
> >
> > const = liftM2 const :: M a -> M b -> M a
> >
> > which I believe should be equivalent to your property.
>
> My belief was wrong, which is evident when using do-notation.
> Kim-Ee stated
>
> do {_ <- b; x <- a; return x} = a
>
> while I examined
>
> do {x <- a; _ <- b; return x} = a
>
> Since do {x <- a; return x} = a holds for any monad, Kim-Ee's property
> can be reduced to
>
> do {_ <- b; a} = a
> or more concisely
> b >> a = a
>
> which I called Kleisli-const in my previous post. As we seemed to have
> settled for "occlusive" I suggest calling
> b >> a = a
> "right-occlusive" or "occlusive from the right" because the right
> action occludes the side-effects of the left action, and
> do {x <- a; _ <- b; return x} = a
> should be called "left-occlusive" or "occlusive from the left" because
> the left action hides the effect of the right action. Under
> commutativity, both are the same but in general these might be
> different properties. I do not have a distinguishing counterexample,
> though, because all monads I come up with are commutative.
>
> David Feuer hinted at the possibility to define occlusiveness more
> generally for Applicative functors. Commutativity might be stated for
> Applicatives as
>
> liftA2 f a b = liftA2 (flip f) b a
>
> So far I can only see two classes of occlusive monads: The reader-like
> (Identity ~ Reader ()) and the set-like monads.
>
> Olaf
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From olf at aatal-apotheke.de  Thu Nov 12 22:26:45 2020
From: olf at aatal-apotheke.de (Olaf Klinke)
Date: Thu, 12 Nov 2020 23:26:45 +0100
Subject: [Haskell-cafe] What to call Occult Effects
In-Reply-To: <CAMgWh9to1TUvEQ=ivfO9areF25Hd+BCvJxWYyQbNTW5k3MQRxw@mail.gmail.com>
References: <8089bc77dacb56f80d05e10a1ce43f37d074b613.camel@aatal-apotheke.de>
 <CAMgWh9to1TUvEQ=ivfO9areF25Hd+BCvJxWYyQbNTW5k3MQRxw@mail.gmail.com>
Message-ID: <0c6beaa8894a8dee6948e63e2df4802929038c18.camel@aatal-apotheke.de>

On Thu, 2020-11-12 at 16:25 -0500, David Feuer wrote:
> First, for clarity, note that
> 
>    const id = flip const
> 
> Consider a (right-)occlusive functor. We immediately see that
> 
> liftA2 (flip const) m (pure x) = pure x
> 
> Using the Applicative laws, we can restate this:
> 
> x <$ m = pure x
> 
> We get the same sort of result for a left-occlusive effect.
> 
> So an occlusive effect can't have any *observable* side effects. It
> must be
> "read only".
> 

I'd rather interpret this as a form of lazyness or call-by-need: If the
action's return value is not used, then the side-effects are also not
executed. Computationally, constant-ness of a function is an
undecidable property. Therefore it is questionable whether any
implementation can exhibit this sort of lazyness with side-effectful
actions. 

Olaf


From ben.franksen at online.de  Fri Nov 13 10:43:02 2020
From: ben.franksen at online.de (Ben Franksen)
Date: Fri, 13 Nov 2020 11:43:02 +0100
Subject: [Haskell-cafe] caching ~/.cabal with github actions on windows
Message-ID: <rolnvm$s4c$1@ciao.gmane.io>

I can't get this to work. It works perfectly fine on Linux and MacOS but
on Windows cabal always re-builds all the dependencies. The cache
post-action on Windows tells me that the cache hasn't changed, which
means cabal actually re-created the ~/.cabal directory exactly as it was
in the cache!

Is this a known bug in cabal on Windows?

Does anyone have a work-around?

Cheers
Ben


From oleg.grenrus at iki.fi  Fri Nov 13 10:54:52 2020
From: oleg.grenrus at iki.fi (Oleg Grenrus)
Date: Fri, 13 Nov 2020 12:54:52 +0200
Subject: [Haskell-cafe] caching ~/.cabal with github actions on windows
In-Reply-To: <rolnvm$s4c$1@ciao.gmane.io>
References: <rolnvm$s4c$1@ciao.gmane.io>
Message-ID: <e14cb051-b22a-e415-1a6c-872031e380a3@iki.fi>

cabal-install doesn't use ~/.cabal on Windows.

See
https://hackage.haskell.org/package/directory-1.3.6.1/docs/System-Directory.html#v:getAppUserDataDirectory

- Oleg

On 13.11.2020 12.43, Ben Franksen wrote:
> I can't get this to work. It works perfectly fine on Linux and MacOS but
> on Windows cabal always re-builds all the dependencies. The cache
> post-action on Windows tells me that the cache hasn't changed, which
> means cabal actually re-created the ~/.cabal directory exactly as it was
> in the cache!
>
> Is this a known bug in cabal on Windows?
>
> Does anyone have a work-around?
>
> Cheers
> Ben
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.

From melkon.or at gmail.com  Fri Nov 13 11:13:09 2020
From: melkon.or at gmail.com (Orestis Melkonian)
Date: Fri, 13 Nov 2020 13:13:09 +0200
Subject: [Haskell-cafe] caching ~/.cabal with github actions on windows
In-Reply-To: <e14cb051-b22a-e415-1a6c-872031e380a3@iki.fi>
References: <rolnvm$s4c$1@ciao.gmane.io>
 <e14cb051-b22a-e415-1a6c-872031e380a3@iki.fi>
Message-ID: <b2632245-4a24-6585-d8ba-642c39624fb4@gmail.com>

Note that if you use the setup-haskell action 
(https://github.com/actions/setup-haskell), you can get the directory 
from its outputs, i.e. `${{ 
steps.setup-haskell-cabal.outputs.cabal-store }}`.

Cheers,
--OM

On 11/13/20 12:54 PM, Oleg Grenrus wrote:
> cabal-install doesn't use ~/.cabal on Windows.
>
> See
> https://hackage.haskell.org/package/directory-1.3.6.1/docs/System-Directory.html#v:getAppUserDataDirectory
>
> - Oleg
>
> On 13.11.2020 12.43, Ben Franksen wrote:
>> I can't get this to work. It works perfectly fine on Linux and MacOS but
>> on Windows cabal always re-builds all the dependencies. The cache
>> post-action on Windows tells me that the cache hasn't changed, which
>> means cabal actually re-created the ~/.cabal directory exactly as it was
>> in the cache!
>>
>> Is this a known bug in cabal on Windows?
>>
>> Does anyone have a work-around?
>>
>> Cheers
>> Ben
>>
>> _______________________________________________
>> Haskell-Cafe mailing list
>> To (un)subscribe, modify options or view archives go to:
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>> Only members subscribed via the mailman list are allowed to post.
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From ben.franksen at online.de  Fri Nov 13 11:32:56 2020
From: ben.franksen at online.de (Ben Franksen)
Date: Fri, 13 Nov 2020 12:32:56 +0100
Subject: [Haskell-cafe] caching ~/.cabal with github actions on windows
In-Reply-To: <e14cb051-b22a-e415-1a6c-872031e380a3@iki.fi>
References: <rolnvm$s4c$1@ciao.gmane.io>
 <e14cb051-b22a-e415-1a6c-872031e380a3@iki.fi>
Message-ID: <rolqt8$bvf$1@ciao.gmane.io>

Am 13.11.20 um 11:54 schrieb Oleg Grenrus:
> cabal-install doesn't use ~/.cabal on Windows.
> 
> See
> https://hackage.haskell.org/package/directory-1.3.6.1/docs/System-Directory.html#v:getAppUserDataDirectory

Thanks. I already suspected that was causing the problem, so I tried to
set CABAL_DIR to a fixed location (and cache that instead):

    env:
      CABAL_DIR: ${{ github.workspace }}/dot-cabal

Again, this works fine on Linux and MacOS but not on Windows.

Cheers
Ben


From ben.franksen at online.de  Fri Nov 13 11:35:49 2020
From: ben.franksen at online.de (Ben Franksen)
Date: Fri, 13 Nov 2020 12:35:49 +0100
Subject: [Haskell-cafe] caching ~/.cabal with github actions on windows
In-Reply-To: <b2632245-4a24-6585-d8ba-642c39624fb4@gmail.com>
References: <rolnvm$s4c$1@ciao.gmane.io>
 <e14cb051-b22a-e415-1a6c-872031e380a3@iki.fi>
 <b2632245-4a24-6585-d8ba-642c39624fb4@gmail.com>
Message-ID: <rolr2l$bvf$2@ciao.gmane.io>

Am 13.11.20 um 12:13 schrieb Orestis Melkonian:
> Note that if you use the setup-haskell action
> (https://github.com/actions/setup-haskell), you can get the directory
> from its outputs, i.e. `${{
> steps.setup-haskell-cabal.outputs.cabal-store }}`.

Thanks, I'll try that.

Cheers
Ben


From ben.franksen at online.de  Fri Nov 13 12:12:14 2020
From: ben.franksen at online.de (Ben Franksen)
Date: Fri, 13 Nov 2020 13:12:14 +0100
Subject: [Haskell-cafe] caching ~/.cabal with github actions on windows
In-Reply-To: <rolr2l$bvf$2@ciao.gmane.io>
References: <rolnvm$s4c$1@ciao.gmane.io>
 <e14cb051-b22a-e415-1a6c-872031e380a3@iki.fi>
 <b2632245-4a24-6585-d8ba-642c39624fb4@gmail.com> <rolr2l$bvf$2@ciao.gmane.io>
Message-ID: <rolt6v$sqi$1@ciao.gmane.io>

Am 13.11.20 um 12:35 schrieb Ben Franksen:
> Am 13.11.20 um 12:13 schrieb Orestis Melkonian:
>> Note that if you use the setup-haskell action
>> (https://github.com/actions/setup-haskell), you can get the directory
>> from its outputs, i.e. `${{
>> steps.setup-haskell-cabal.outputs.cabal-store }}`.
> 
> Thanks, I'll try that.

It hasn't completed but looks pretty good. In fact the cabal store path
gets shown as

    path: C:\sr

I would never have guessed that path, nor did I see it in the cabal docs.

(BTW, the "setup-haskell-cabal" in your reply is the id: that you have
given your setup-haskell step; it took me a while to figure that out
since I am pretty new to github actions).

Thanks again
Ben


From ben.franksen at online.de  Fri Nov 13 12:23:35 2020
From: ben.franksen at online.de (Ben Franksen)
Date: Fri, 13 Nov 2020 13:23:35 +0100
Subject: [Haskell-cafe] caching ~/.cabal with github actions on windows
In-Reply-To: <rolt6v$sqi$1@ciao.gmane.io>
References: <rolnvm$s4c$1@ciao.gmane.io>
 <e14cb051-b22a-e415-1a6c-872031e380a3@iki.fi>
 <b2632245-4a24-6585-d8ba-642c39624fb4@gmail.com> <rolr2l$bvf$2@ciao.gmane.io>
 <rolt6v$sqi$1@ciao.gmane.io>
Message-ID: <rolts7$s4s$1@ciao.gmane.io>

Caching works now and re-running the job gets it down to 2 minutes (from
15 for the first run).

Awful! Thanks!

Cheers
Ben

Am 13.11.20 um 13:12 schrieb Ben Franksen:
> Am 13.11.20 um 12:35 schrieb Ben Franksen:
>> Am 13.11.20 um 12:13 schrieb Orestis Melkonian:
>>> Note that if you use the setup-haskell action
>>> (https://github.com/actions/setup-haskell), you can get the directory
>>> from its outputs, i.e. `${{
>>> steps.setup-haskell-cabal.outputs.cabal-store }}`.
>>
>> Thanks, I'll try that.
> 
> It hasn't completed but looks pretty good. In fact the cabal store path
> gets shown as
> 
>     path: C:\sr
> 
> I would never have guessed that path, nor did I see it in the cabal docs.
> 
> (BTW, the "setup-haskell-cabal" in your reply is the id: that you have
> given your setup-haskell step; it took me a while to figure that out
> since I am pretty new to github actions).
> 
> Thanks again
> Ben
> 
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
> 



From sergey.goncharov at fau.de  Fri Nov 13 14:22:20 2020
From: sergey.goncharov at fau.de (Sergey Goncharov)
Date: Fri, 13 Nov 2020 15:22:20 +0100
Subject: [Haskell-cafe] What to call Occult Effects
In-Reply-To: <8089bc77dacb56f80d05e10a1ce43f37d074b613.camel@aatal-apotheke.de>
Message-ID: <15162dad-3b29-680e-696c-c05a21ea8dc2@fau.de>

Dear Olaf and everyone,

the law do {_ <- b; a} = a is equivalent to do {_ <- b; return ()} = return (), for, assuming the latter,

	  do {_ <- b; a}
  	= do {_ <- do {_ <- b; return ()}; a}
  	= do {_ <- return (); a}
	= a

and it does actually have some history. It was dubbed 'discardability' by Thielecke [1] and explored by 
Führmann in [2] together with some other important properties of effects, such as 'centrality' and 
'commutativity'. Combinations of these properties and examples are explored in the conventional 
Haskell-like style in [3] (where 'discardability' is called 'side-effect freeness' though).

Cheers,
Sergey

[1] H. Thielecke, Categorical structure of continuation passing style, Ph.D. Thesis, University of 
Edinburgh, 1997.

[2] C. Führmann, Varieties of effects, in: M. Nielsen, U. Engberg (Eds.), Foundations of Software 
Science and Computation Structures, FOSSACS 2002, in: Lect. Notes Comput. Sci., vol. 2303, Springer, 
2002, pp. 144–158.

[3] L. Schröder, T. Mossakowski, Monad-independent dynamic logic in HasCasl, J. Logic Comput. 14 (2004) 
571–619

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From ida.bzowska at gmail.com  Fri Nov 13 16:24:03 2020
From: ida.bzowska at gmail.com (Ida Bzowska)
Date: Fri, 13 Nov 2020 17:24:03 +0100
Subject: [Haskell-cafe]  Advent of Haskell is still waiting for ideas
Message-ID: <CAOOeZjDRQmYyrgei0ZNM3CUS7WVkBOh2+4Fxk9mfYLFT8nvijA@mail.gmail.com>

Hi there,

Advent of Haskell is an advent calendar filled with Haskell content,
obviously :)
The first confirmations to "Advent of Haskell" participants' have been sent
this week, but there are still a lot of open spots to go, so do not
hesitate to submit your idea.
All the details are available here: https://adventofhaskell.com

Happy haskelling everyone!

λCheers,
Ida
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From olf at aatal-apotheke.de  Fri Nov 13 21:07:07 2020
From: olf at aatal-apotheke.de (Olaf Klinke)
Date: Fri, 13 Nov 2020 22:07:07 +0100
Subject: [Haskell-cafe] What to call Occult Effects
In-Reply-To: <CAMgWh9to1TUvEQ=ivfO9areF25Hd+BCvJxWYyQbNTW5k3MQRxw@mail.gmail.com>
References: <8089bc77dacb56f80d05e10a1ce43f37d074b613.camel@aatal-apotheke.de>
 <CAMgWh9to1TUvEQ=ivfO9areF25Hd+BCvJxWYyQbNTW5k3MQRxw@mail.gmail.com>
Message-ID: <02ebee63290ca8176791eb2f7bbb721537ff94c3.camel@aatal-apotheke.de>

Here is a shorter proof that right-occlusive implies left-occlusive. 

  b >>= const a
= join (fmap  (const  a) b)     monad law (=<<) = (join.).fmap
= join (const (return a) b)     assumption: left-occlusive
= join (return a)
= a                             monad law join.return = id

I still don't know whether right-occlusive implies left-occlusive. 
But I found a non-commutative monad which is not a reader monad and
which is left-occlusive: the Set monad from the infinite-search package
[1]. This monad is non-trivial and quite obviously satisfies 
fmap.const = const.return
when you look at the source of the Functor instance. I verified by
timing search over a vast and a tiny Set. 

In accordance with your arguments, I am beginning to think that 
b >> a = a
could be taken as a _definition_ of a side-effect-free monad. 

Cheers, 
Olaf

[1] http://hackage.haskell.org/package/infinite-search

On Thu, 2020-11-12 at 16:25 -0500, David Feuer wrote:
> First, for clarity, note that
> 
>    const id = flip const
> 
> Consider a (right-)occlusive functor. We immediately see that
> 
> liftA2 (flip const) m (pure x) = pure x
> 
> Using the Applicative laws, we can restate this:
> 
> x <$ m = pure x
> 
> We get the same sort of result for a left-occlusive effect.
> 
> So an occlusive effect can't have any *observable* side effects. It
> must be
> "read only".
> 
> On Thu, Nov 12, 2020, 3:59 PM Olaf Klinke <olf at aatal-apotheke.de>
> wrote:
> 
> > > First, instead of `const id` I will use `const`, that is, we
> > > shall
> > > prove
> > > 
> > > const = liftM2 const :: M a -> M b -> M a
> > > 
> > > which I believe should be equivalent to your property.
> > 
> > My belief was wrong, which is evident when using do-notation.
> > Kim-Ee stated
> > 
> > do {_ <- b; x <- a; return x} = a
> > 
> > while I examined
> > 
> > do {x <- a; _ <- b; return x} = a
> > 
> > Since do {x <- a; return x} = a holds for any monad, Kim-Ee's
> > property
> > can be reduced to
> > 
> > do {_ <- b; a} = a
> > or more concisely
> > b >> a = a
> > 
> > which I called Kleisli-const in my previous post. As we seemed to
> > have
> > settled for "occlusive" I suggest calling
> > b >> a = a
> > "right-occlusive" or "occlusive from the right" because the right
> > action occludes the side-effects of the left action, and
> > do {x <- a; _ <- b; return x} = a
> > should be called "left-occlusive" or "occlusive from the left"
> > because
> > the left action hides the effect of the right action. Under
> > commutativity, both are the same but in general these might be
> > different properties. I do not have a distinguishing
> > counterexample,
> > though, because all monads I come up with are commutative.
> > 
> > David Feuer hinted at the possibility to define occlusiveness more
> > generally for Applicative functors. Commutativity might be stated
> > for
> > Applicatives as
> > 
> > liftA2 f a b = liftA2 (flip f) b a
> > 
> > So far I can only see two classes of occlusive monads: The reader-
> > like
> > (Identity ~ Reader ()) and the set-like monads.
> > 
> > Olaf
> > 
> > _______________________________________________
> > Haskell-Cafe mailing list
> > To (un)subscribe, modify options or view archives go to:
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> > Only members subscribed via the mailman list are allowed to post.


From nadine.and.henry at pobox.com  Sat Nov 14 04:08:46 2020
From: nadine.and.henry at pobox.com (Henry Laxen)
Date: Fri, 13 Nov 2020 20:08:46 -0800
Subject: [Haskell-cafe] Generic Sorting
Message-ID: <24495.22606.60949.58172@gargle.gargle.HOWL>

Good evening Haskellers.

I've done some searching but so far haven't found anything, which make
me think this probably isn't possible.  I am wondering if it is
possible to do a "Generic Sort" on multilevel data structures.
Suppose you have something like:

data A = A Int [Int]
data B = B Int [A]

a1 = A 2 [2,1]
a2 = A 1 [4,3]
b  = B 1 [a1,a2]

genericSort b = B 1 [A 1 [3,4], A 2 [1,2]]

note that not only are the A's sorted, but the list inside each A is
sorted.  It "sorted all the way down".  Has Edward written such a
thing yet? ;-) His "discrimination" library doesn't do this, in case
you're wondering.  Any ideas?

Best wishes,
Henry Laxen

From rae at richarde.dev  Sat Nov 14 04:11:21 2020
From: rae at richarde.dev (Richard Eisenberg)
Date: Sat, 14 Nov 2020 04:11:21 +0000
Subject: [Haskell-cafe] support for ergonomic dependent types
Message-ID: <010f0175c4f350f8-a09af29c-61d1-48ef-93e6-1d2f2fc06b1f-000000@us-east-2.amazonses.com>

Hi all,

The GHC Steering Committee has been struggling recently to decide on several related proposals. The struggle is all around whether we should favor making a design that is future-compatible with dependent types, or favor a design that is more cohesive with e.g. Haskell98. (Sometimes, we can have both. Those are good times.) This isn't about backward compatibility -- the design for dependent Haskell is fully backward compatible with Haskell98. It's more about how well the new features fit with the old ones.

To clarify our thinking on it all, I've made a new proposal to discuss whether or not we want to favor keeping an avenue open to ergonomic dependent types in the future. If you have an opinion, please express it on the proposal. In particular, if you care about the possibility of ergonomic dependent types in Haskell, now is the time to show that support by thumbs-upping the proposal.

The proposal is at https://github.com/ghc-proposals/ghc-proposals/pull/378.

Thanks!
Richard

From jack at jackkelly.name  Sat Nov 14 04:36:57 2020
From: jack at jackkelly.name (jack at jackkelly.name)
Date: Sat, 14 Nov 2020 04:36:57 +0000
Subject: [Haskell-cafe] Generic Sorting
In-Reply-To: <24495.22606.60949.58172@gargle.gargle.HOWL>
References: <24495.22606.60949.58172@gargle.gargle.HOWL>
Message-ID: <f2131b2a3c8eb47f94413788dbeb47c6@jackkelly.name>

November 14, 2020 2:08 PM, "Henry Laxen" <nadine.and.henry at pobox.com> wrote:

> I've done some searching but so far haven't found anything, which make
> me think this probably isn't possible. I am wondering if it is
> possible to do a "Generic Sort" on multilevel data structures.
> Suppose you have something like:

This is not quite what you asked for, but might get you started. It's based on a trick that Alex Mason once showed me:

{-# LANGUAGE AllowAmbiguousTypes  #-}
{-# LANGUAGE DeriveDataTypeable  #-}
{-# LANGUAGE ScopedTypeVariables #-}

import Control.Lens
import Data.Data
import Data.Data.Lens
import Data.List

data A = A Int [Int] deriving (Data, Show)
data B = B Int [A] deriving (Data, Show)

a1 = A 2 [2,1]
a2 = A 1 [4,3]
b  = B 1 [a1,a2]

-- | oh no
-- >>> genericSort @Int b
-- B 1 [A 1 [1,2],A 2 [3,4]]
genericSort :: forall a d . (Data d, Typeable a, Ord a) => d -> d
genericSort = partsOf template %~ (sort :: [a] -> [a])

Note that it's sorted every Int anywhere in the structure, not just the ones inside an A.

HTH,
-- Jack

From lemming at henning-thielemann.de  Sat Nov 14 08:11:46 2020
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sat, 14 Nov 2020 09:11:46 +0100 (CET)
Subject: [Haskell-cafe] Generic Sorting
In-Reply-To: <24495.22606.60949.58172@gargle.gargle.HOWL>
References: <24495.22606.60949.58172@gargle.gargle.HOWL>
Message-ID: <alpine.DEB.2.20.2011140907390.5806@sputnik>


On Fri, 13 Nov 2020, Henry Laxen wrote:

> Good evening Haskellers.
>
> I've done some searching but so far haven't found anything, which make
> me think this probably isn't possible.  I am wondering if it is
> possible to do a "Generic Sort" on multilevel data structures.
> Suppose you have something like:
>
> data A = A Int [Int]
> data B = B Int [A]
>
> a1 = A 2 [2,1]
> a2 = A 1 [4,3]
> b  = B 1 [a1,a2]
>
> genericSort b = B 1 [A 1 [3,4], A 2 [1,2]]
>
> note that not only are the A's sorted, but the list inside each A is
> sorted.  It "sorted all the way down".  Has Edward written such a
> thing yet? ;-) His "discrimination" library doesn't do this, in case
> you're wondering.  Any ideas?

You could first sort the structures and then fill it with a sorted 
flattened list.

From mlang at blind.guru  Sat Nov 14 15:32:22 2020
From: mlang at blind.guru (Mario Lang)
Date: Sat, 14 Nov 2020 16:32:22 +0100
Subject: [Haskell-cafe] Reading Haddock sources on hackage no longer
 possible with simple browsers?
Message-ID: <87a6vk6jjt.fsf@blind.guru>

Hi.

I have been using Lynx to read stuff on hacakge for a long time.

I recently noticed that it is no longer possible to read the source of a
module, because extra type information (which is likely hidden in a
modern browser) is inline with the actual sources.  This makes the go to
source feature effectively useless.  An example (from the ISBN package):

    deriving (Int -> ISBN -> ShowS
    [ISBN] -> ShowS
    ISBN -> String
    (Int -> ISBN -> ShowS)
    -> (ISBN -> String) -> ([ISBN] -> ShowS) -> Show ISBN
    forall a.
    (Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
    showList :: [ISBN] -> ShowS
    $cshowList :: [ISBN] -> ShowS
    show :: ISBN -> String
    $cshow :: ISBN -> String
    showsPrec :: Int -> ISBN -> ShowS
    $cshowsPrec :: Int -> ISBN -> ShowS
    Show, ISBN -> ISBN -> Bool
    (ISBN -> ISBN -> Bool) -> (ISBN -> ISBN -> Bool) -> Eq ISBN
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    /= :: ISBN -> ISBN -> Bool
    $c/= :: ISBN -> ISBN -> Bool
    == :: ISBN -> ISBN -> Bool
    $c== :: ISBN -> ISBN -> Bool
    Eq)
    
I know Haskell has a ton of extensions, but I am pretty sure nobody
writes code like this :-)

This is, frankly, pretty horrible.   Can something be done to fix this?

(I am aware that certain modernisations are unstoppable.  However, this
one looks like a bug.)

-- 
CYa,
  ⡍⠁⠗⠊⠕

From nadine.and.henry at pobox.com  Sat Nov 14 17:30:52 2020
From: nadine.and.henry at pobox.com (Henry Laxen)
Date: Sat, 14 Nov 2020 09:30:52 -0800
Subject: [Haskell-cafe] Generic Sorting
In-Reply-To: <f2131b2a3c8eb47f94413788dbeb47c6@jackkelly.name>
References: <24495.22606.60949.58172@gargle.gargle.HOWL>
 <f2131b2a3c8eb47f94413788dbeb47c6@jackkelly.name>
Message-ID: <24496.5196.109558.32813@gargle.gargle.HOWL>

>>>>> "jack" == jack  <jack at jackkelly.name> writes:

    Henry> November 14, 2020 2:08 PM, "Henry Laxen" <nadine.and.henry at pobox.com> wrote:
    Henry> I've done some searching but so far haven't found anything, which make
    Henry> me think this probably isn't possible. I am wondering if it is
    Henry> possible to do a "Generic Sort" on multilevel data structures.
    Henry> Suppose you have something like:

    jack> This is not quite what you asked for, but might get you started. It's based on a trick that Alex Mason once showed me:

    jack> {-# LANGUAGE AllowAmbiguousTypes  #-}
    jack> {-# LANGUAGE DeriveDataTypeable  #-}
    jack> {-# LANGUAGE ScopedTypeVariables #-}

    jack> import Control.Lens
    jack> import Data.Data
    jack> import Data.Data.Lens
    jack> import Data.List

    jack> data A = A Int [Int] deriving (Data, Show)
    jack> data B = B Int [A] deriving (Data, Show)

    jack> a1 = A 2 [2,1]
    jack> a2 = A 1 [4,3]
    jack> b  = B 1 [a1,a2]

    jack> -- | oh no
    jack> -- >>> genericSort @Int b
    jack> -- B 1 [A 1 [1,2],A 2 [3,4]]
    jack> genericSort :: forall a d . (Data d, Typeable a, Ord a) => d -> d
    jack> genericSort = partsOf template %~ (sort :: [a] -> [a])

    Henry> Note that it's sorted every Int anywhere in the structure, not just the ones inside an A.

Wow Jack, that looks like magic.  I'm going to read about partsOf and
template, which I've never used before.  One thing, to actuall run it you need
to add {-# LANGUAGE TypeApplications #-} so you can say "genericSort @Int b".
Thanks so much for your quick and brilliant response.
Best wishes,
Henry Laxen

From johannes.waldmann at htwk-leipzig.de  Sat Nov 14 18:01:47 2020
From: johannes.waldmann at htwk-leipzig.de (Johannes Waldmann)
Date: Sat, 14 Nov 2020 19:01:47 +0100
Subject: [Haskell-cafe] Reading Haddock sources on hackage no longer
 possible with simple browsers?
Message-ID: <216b0636-c259-400d-ef8e-7226da3e08f9@htwk-leipzig.de>

> I recently noticed that it is no longer possible
> to read the source of a module, because extra type information
> (which is likely hidden in a modern browser)
> is inline with the actual sources.

I confirmed your example, reading with lynx and w3m.

It seems the extra text
is the methods of the type classes (mentioned after "deriving")
and it gets shown on on mouse-over in a graphical browser.

(Re: "nobody writes code like this" - the compiler does?
Some methods here seem auto-generated.)

Looks like a bug in haddock, then? (Or in lynx' handling of CSS?)
The actual HTML source looks legit, at least partially
(see example below)

This seems related:
https://github.com/haskell/haddock/pull/1197

I will open an issue on accessibility.

- J.W.

<span class="hs-keyword">deriving</span><span> </span><span
class="hs-special">(</span><span id="local-6989586621679046279"><span
id="local-6989586621679046281"><span
id="local-6989586621679046283"><span class="annot"><span
class="annottext">Int -&gt; ISBN -&gt; ShowS
[ISBN] -&gt; ShowS
ISBN -&gt; String
(Int -&gt; ISBN -&gt; ShowS)
-&gt; (ISBN -&gt; String) -&gt; ([ISBN] -&gt; ShowS) -&gt; Show ISBN
forall a.
(Int -&gt; a -&gt; ShowS) -&gt; (a -&gt; String) -&gt; ([a] -&gt; ShowS)
-&gt; Show a
showList :: [ISBN] -&gt; ShowS
$cshowList :: [ISBN] -&gt; ShowS
show :: ISBN -&gt; String
$cshow :: ISBN -&gt; String
showsPrec :: Int -&gt; ISBN -&gt; ShowS
$cshowsPrec :: Int -&gt; ISBN -&gt; ShowS
</span><span class="hs-identifier hs-var hs-var hs-var hs-var hs-var
hs-var hs-var hs-var">Show</span>


From lysxia at gmail.com  Sat Nov 14 18:12:10 2020
From: lysxia at gmail.com (Li-yao Xia)
Date: Sat, 14 Nov 2020 13:12:10 -0500
Subject: [Haskell-cafe] Reading Haddock sources on hackage no longer
 possible with simple browsers?
In-Reply-To: <87a6vk6jjt.fsf@blind.guru>
References: <87a6vk6jjt.fsf@blind.guru>
Message-ID: <5539a15f-4fb2-8d4f-d7da-d325d16727a9@gmail.com>

Note that the raw sources are available in another location:

https://hackage.haskell.org/package/isbn-1.1.0.2/src/lib/Data/ISBN/Types.hs

(starting from the Hackage page for the package, under Downloads, click 
"browse")

On 11/14/2020 10:32 AM, Mario Lang wrote:
> Hi.
> 
> I have been using Lynx to read stuff on hacakge for a long time.
> 
> I recently noticed that it is no longer possible to read the source of a
> module, because extra type information (which is likely hidden in a
> modern browser) is inline with the actual sources.  This makes the go to
> source feature effectively useless.  An example (from the ISBN package):
> 
>      deriving (Int -> ISBN -> ShowS
>      [ISBN] -> ShowS
>      ISBN -> String
>      (Int -> ISBN -> ShowS)
>      -> (ISBN -> String) -> ([ISBN] -> ShowS) -> Show ISBN
>      forall a.
>      (Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
>      showList :: [ISBN] -> ShowS
>      $cshowList :: [ISBN] -> ShowS
>      show :: ISBN -> String
>      $cshow :: ISBN -> String
>      showsPrec :: Int -> ISBN -> ShowS
>      $cshowsPrec :: Int -> ISBN -> ShowS
>      Show, ISBN -> ISBN -> Bool
>      (ISBN -> ISBN -> Bool) -> (ISBN -> ISBN -> Bool) -> Eq ISBN
>      forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
>      /= :: ISBN -> ISBN -> Bool
>      $c/= :: ISBN -> ISBN -> Bool
>      == :: ISBN -> ISBN -> Bool
>      $c== :: ISBN -> ISBN -> Bool
>      Eq)
>      
> I know Haskell has a ton of extensions, but I am pretty sure nobody
> writes code like this :-)
> 
> This is, frankly, pretty horrible.   Can something be done to fix this?
> 
> (I am aware that certain modernisations are unstoppable.  However, this
> one looks like a bug.)
> 

From alec.theriault at gmail.com  Sat Nov 14 18:16:24 2020
From: alec.theriault at gmail.com (Alec Theriault)
Date: Sat, 14 Nov 2020 13:16:24 -0500
Subject: [Haskell-cafe] Reading Haddock sources on hackage no longer
 possible with simple browsers?
In-Reply-To: <216b0636-c259-400d-ef8e-7226da3e08f9@htwk-leipzig.de>
References: <216b0636-c259-400d-ef8e-7226da3e08f9@htwk-leipzig.de>
Message-ID: <5184D544-1752-4F60-8B09-2CD019EA552B@gmail.com>

Hello,

This is indeed by design - it is a relatively new Haddock feature (here’s the original issue <https://github.com/haskell/haddock/issues/715>) where types of identifiers and identifiers bound are shown on mouse-over.
Here is what this looks like in a graphical browser:



As for the the weird declarations like $cshowList and company, this seems to be a bug - Haddock should not display those identifiers.

Although I’m sympathetic to the accessibility, in this case wouldn’t just directly opening the sources (in a text editor) be simpler? Is there a (simple) way to preserve the experience when browsing using Lynx without also holding back features aimed at a regular browsing experience?

Alec

> On Nov 14, 2020, at 1:01 PM, Johannes Waldmann <johannes.waldmann at htwk-leipzig.de> wrote:
> 
>> I recently noticed that it is no longer possible
>> to read the source of a module, because extra type information
>> (which is likely hidden in a modern browser)
>> is inline with the actual sources.
> 
> I confirmed your example, reading with lynx and w3m.
> 
> It seems the extra text
> is the methods of the type classes (mentioned after "deriving")
> and it gets shown on on mouse-over in a graphical browser.
> 
> (Re: "nobody writes code like this" - the compiler does?
> Some methods here seem auto-generated.)
> 
> Looks like a bug in haddock, then? (Or in lynx' handling of CSS?)
> The actual HTML source looks legit, at least partially
> (see example below)
> 
> This seems related:
> https://github.com/haskell/haddock/pull/1197
> 
> I will open an issue on accessibility.
> 
> - J.W.
> 
> <span class="hs-keyword">deriving</span><span> </span><span
> class="hs-special">(</span><span id="local-6989586621679046279"><span
> id="local-6989586621679046281"><span
> id="local-6989586621679046283"><span class="annot"><span
> class="annottext">Int -&gt; ISBN -&gt; ShowS
> [ISBN] -&gt; ShowS
> ISBN -&gt; String
> (Int -&gt; ISBN -&gt; ShowS)
> -&gt; (ISBN -&gt; String) -&gt; ([ISBN] -&gt; ShowS) -&gt; Show ISBN
> forall a.
> (Int -&gt; a -&gt; ShowS) -&gt; (a -&gt; String) -&gt; ([a] -&gt; ShowS)
> -&gt; Show a
> showList :: [ISBN] -&gt; ShowS
> $cshowList :: [ISBN] -&gt; ShowS
> show :: ISBN -&gt; String
> $cshow :: ISBN -&gt; String
> showsPrec :: Int -&gt; ISBN -&gt; ShowS
> $cshowsPrec :: Int -&gt; ISBN -&gt; ShowS
> </span><span class="hs-identifier hs-var hs-var hs-var hs-var hs-var
> hs-var hs-var hs-var">Show</span>
> 
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.

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From johannes.waldmann at htwk-leipzig.de  Sat Nov 14 18:24:55 2020
From: johannes.waldmann at htwk-leipzig.de (Johannes Waldmann)
Date: Sat, 14 Nov 2020 19:24:55 +0100
Subject: [Haskell-cafe] Reading Haddock sources on hackage no longer
 possible with simple browsers?
In-Reply-To: <5184D544-1752-4F60-8B09-2CD019EA552B@gmail.com>
References: <216b0636-c259-400d-ef8e-7226da3e08f9@htwk-leipzig.de>
 <5184D544-1752-4F60-8B09-2CD019EA552B@gmail.com>
Message-ID: <105add9a-5f7d-0fe1-e532-74633994f3a9@htwk-leipzig.de>


>  ... a (simple) way to preserve the experience when browsing using Lynx

yes, that is the question. What *is* the recommended way
of providing a tooltip-like experience for text browsers?

- J.

From mlang at blind.guru  Sun Nov 15 00:18:51 2020
From: mlang at blind.guru (Mario Lang)
Date: Sun, 15 Nov 2020 01:18:51 +0100
Subject: [Haskell-cafe] Reading Haddock sources on hackage no longer
 possible with simple browsers?
In-Reply-To: <5184D544-1752-4F60-8B09-2CD019EA552B@gmail.com> (Alec
 Theriault's message of "Sat, 14 Nov 2020 13:16:24 -0500")
References: <216b0636-c259-400d-ef8e-7226da3e08f9@htwk-leipzig.de>
 <5184D544-1752-4F60-8B09-2CD019EA552B@gmail.com>
Message-ID: <875z6779qs.fsf@blind.guru>

Alec Theriault <alec.theriault at gmail.com> writes:

> Although I’m sympathetic to the accessibility, in this case wouldn’t just
> directly opening the sources (in a text editor) be simpler?

Following a link to a definition is convenient because there is an
anchor.
Of course I can just open the original sources in a text editor.
But then I am no longer reading documentation, I am reading sources!

> Is there a (simple) way to preserve the experience when browsing using
> Lynx without also holding back features aimed at a regular browsing
> experience?

I was expecting this sort of killer argument.  I have to admit I am too
exhausted with this topic to try and give a meaningful answer.  There
used to be a time when compatibility to existing technology was a goal
by itself.  This is going away even in circles which usually have tried
to achieve some sort of technical excellence.  I am sad.  But I can not
do anything against the tides except for sometimes pointing at ships
while they are sinking, hoping to get someone to see reason and rescue
at least some of them.

Practically speaking, the problem is the visibility style attribute.  As
far as I know, none of the text browsers (lynx, w3m, elinks, eww) have
CSS support.  Barring any other HTML construct which would allow to hide
things by default for text browsers, all I can think of a plain
version in addition to a hip version.  That should be easy to
autogenerate, but it has all the problems attached to a alternative
version.

-- 
CYa,
  ⡍⠁⠗⠊⠕

From evincarofautumn at gmail.com  Sun Nov 15 04:25:44 2020
From: evincarofautumn at gmail.com (Jon Purdy)
Date: Sat, 14 Nov 2020 20:25:44 -0800
Subject: [Haskell-cafe] Reading Haddock sources on hackage no longer
 possible with simple browsers?
In-Reply-To: <875z6779qs.fsf@blind.guru>
References: <216b0636-c259-400d-ef8e-7226da3e08f9@htwk-leipzig.de>
 <5184D544-1752-4F60-8B09-2CD019EA552B@gmail.com> <875z6779qs.fsf@blind.guru>
Message-ID: <CAE3FWBvUV7kfK09mWAoCRD-w=WK70DW2oxW8hU8+w3MO3MmrVA@mail.gmail.com>

(Neglected to CC haskell-cafe, sorry Mario for the duplicate.)

The only plain-HTML solutions I’m aware of are the ‘title’ attribute and
the HTML5 ‘<details>’ element. The latter may contain a ‘<summary>’ element
for the content displayed by default, plus other content that the user can
expand or collapse. Unfortunately, as far as I know Lynx doesn’t support
either of these; not sure about other text browsers. In Lynx you could
maybe get some nice UX for this with the ‘<fn>’ footnote element from HTML
3.0, but that’s deprecated and probably not supported in other browsers.

It doesn’t help with Lynx support, but I guess the right thing to do here
for screenreader support in other browsers is to add the ‘tooltip’ role to
the tooltip element, toggle its ‘hidden’ attribute with JavaScript to show
and hide it, and use ‘aria-describedby’ / ‘aria-expanded’ on the anchor
element to handle relating the two and announcing the tooltip correctly
when it’s shown.


On Sat, Nov 14, 2020 at 4:20 PM Mario Lang <mlang at blind.guru> wrote:

> Alec Theriault <alec.theriault at gmail.com> writes:
>
> > Although I’m sympathetic to the accessibility, in this case wouldn’t just
> > directly opening the sources (in a text editor) be simpler?
>
> Following a link to a definition is convenient because there is an
> anchor.
> Of course I can just open the original sources in a text editor.
> But then I am no longer reading documentation, I am reading sources!
>
> > Is there a (simple) way to preserve the experience when browsing using
> > Lynx without also holding back features aimed at a regular browsing
> > experience?
>
> I was expecting this sort of killer argument.  I have to admit I am too
> exhausted with this topic to try and give a meaningful answer.  There
> used to be a time when compatibility to existing technology was a goal
> by itself.  This is going away even in circles which usually have tried
> to achieve some sort of technical excellence.  I am sad.  But I can not
> do anything against the tides except for sometimes pointing at ships
> while they are sinking, hoping to get someone to see reason and rescue
> at least some of them.
>
> Practically speaking, the problem is the visibility style attribute.  As
> far as I know, none of the text browsers (lynx, w3m, elinks, eww) have
> CSS support.  Barring any other HTML construct which would allow to hide
> things by default for text browsers, all I can think of a plain
> version in addition to a hip version.  That should be easy to
> autogenerate, but it has all the problems attached to a alternative
> version.
>
> --
> CYa,
>   ⡍⠁⠗⠊⠕
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From tikhon at jelv.is  Sun Nov 15 05:42:28 2020
From: tikhon at jelv.is (Tikhon Jelvis)
Date: Sat, 14 Nov 2020 21:42:28 -0800
Subject: [Haskell-cafe] Redirecting hackage.haskell.org to HTTPS
Message-ID: <CAJN5CVK7V1pEDbsq=F5ireqcEaN78pF5-9ThM_YoWJu6Y9gVWA@mail.gmail.com>

 Pages on hackage.haskell.org are currently served over both HTTP and
HTTPS. Package security on Hackage does not depend on HTTPS, so we keep
HTTP endpoints for backwards compatibility with automated systems that
depend on Hackage and do not support HTTPS.

However, this means that it's possible for users to inadvertently browse
Hackage pages on HTTP which is not a great user experience. To address this
issue without breaking existing scripts, we are planning to redirect
requests to HTTPS based on User-Agent headers: requests with "Mozilla/5.0"
in their User-Agent string will be redirected to HTTPS and other requests
will remain unchanged.

Please contact us at committee at haskell.org if this change will cause
problems with how you use Hackage. Otherwise, the new behavior will go into
effect on 2020-11-23.

Thanks!
-Tikhon Jelvis, on behalf of the Haskell.org Committee
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From branimir.maksimovic at gmail.com  Sun Nov 15 05:55:52 2020
From: branimir.maksimovic at gmail.com (Branimir Maksimovic)
Date: Sun, 15 Nov 2020 06:55:52 +0100
Subject: [Haskell-cafe] Redirecting hackage.haskell.org to HTTPS
In-Reply-To: <CAJN5CVK7V1pEDbsq=F5ireqcEaN78pF5-9ThM_YoWJu6Y9gVWA@mail.gmail.com>
References: <CAJN5CVK7V1pEDbsq=F5ireqcEaN78pF5-9ThM_YoWJu6Y9gVWA@mail.gmail.com>
Message-ID: <f6251d1c-0581-ef0a-5e43-9441defb85a9@gmail.com>

So I change user agent signature ;)

Greets, Branimir.

On 11/15/20 6:42 AM, Tikhon Jelvis wrote:
> Pages on hackage.haskell.org <http://hackage.haskell.org> are 
> currently served over both HTTP and HTTPS. Package security on Hackage 
> does not depend on HTTPS, so we keep HTTP endpoints for backwards 
> compatibility with automated systems that depend on Hackage and do not 
> support HTTPS.
>
> However, this means that it's possible for users to inadvertently 
> browse Hackage pages on HTTP which is not a great user experience. To 
> address this issue without breaking existing scripts, we are planning 
> to redirect requests to HTTPS based on User-Agent headers: requests 
> with "Mozilla/5.0" in their User-Agent string will be redirected to 
> HTTPS and other requests will remain unchanged.
>
> Please contact us at 
> committee at haskell.org<mailto:committee at haskell.org> if this change 
> will cause problems with how you use Hackage. Otherwise, the new 
> behavior will go into effect on 2020-11-23.
>
> Thanks!
> -Tikhon Jelvis, on behalf of the Haskell.org Committee
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From m.douglas.mcilroy at dartmouth.edu  Sun Nov 15 15:19:51 2020
From: m.douglas.mcilroy at dartmouth.edu (M Douglas McIlroy)
Date: Sun, 15 Nov 2020 10:19:51 -0500
Subject: [Haskell-cafe] Reading Haddock sources on hackage no longer
	possible with simple browsers?
Message-ID: <CAKH6PiVEJN1oKJ=U+VnkoE-gp0+dDwzh3f8sUymon+==no=mUw@mail.gmail.com>

> I am pretty sure nobody writes code like this

> I confirmed your example, reading with lynx and w3m.

> wouldn’t just directly opening the sources (in a text editor) be simpler? Is there a (simple) way to preserve the experience when browsing using Lynx without also holding back features aimed at a regular browsing experience?

I second that.  I have always been annoyed by the ransom-note
appearance of colorized  listings. But that's just my taste. I
suspect, though, that lots of people have been frustrated when they
discover they can't  use the code they see because it's festooned with
markup. Golang.org offers similar listings, but also provides a button
for selecting the underlying plain text. I would like hackage a lot
better if it did so, too.

Doug

From bob at redivi.com  Sun Nov 15 16:18:24 2020
From: bob at redivi.com (Bob Ippolito)
Date: Sun, 15 Nov 2020 08:18:24 -0800
Subject: [Haskell-cafe] Redirecting hackage.haskell.org to HTTPS
In-Reply-To: <CAJN5CVK7V1pEDbsq=F5ireqcEaN78pF5-9ThM_YoWJu6Y9gVWA@mail.gmail.com>
References: <CAJN5CVK7V1pEDbsq=F5ireqcEaN78pF5-9ThM_YoWJu6Y9gVWA@mail.gmail.com>
Message-ID: <CACwMPm_uhn_QTHXUng3mq95Neo0qCPMXZWBTXvPs0dq-qme_rA@mail.gmail.com>

In addition to the redirect, and for the same reasons, enabling HSTS [1]
and submitting it to the HSTS preload list for browsers [2] may also make
sense. I don't think it should have any effect on agents that are visiting
the HTTP version of the site unless the agent somehow simultaneously
supports HSTS, has the preload list or has previously visited the site on
HTTPS, and can't cope a client-side URL rewrite from HTTP to HTTPS.

[1]
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Strict-Transport-Security
[2] https://hstspreload.org/

-bob

On Sat, Nov 14, 2020 at 9:43 PM Tikhon Jelvis <tikhon at jelv.is> wrote:

> Pages on hackage.haskell.org are currently served over both HTTP and
> HTTPS. Package security on Hackage does not depend on HTTPS, so we keep
> HTTP endpoints for backwards compatibility with automated systems that
> depend on Hackage and do not support HTTPS.
>
> However, this means that it's possible for users to inadvertently browse
> Hackage pages on HTTP which is not a great user experience. To address this
> issue without breaking existing scripts, we are planning to redirect
> requests to HTTPS based on User-Agent headers: requests with "Mozilla/5.0"
> in their User-Agent string will be redirected to HTTPS and other requests
> will remain unchanged.
>
> Please contact us at committee at haskell.org if this change will cause
> problems with how you use Hackage. Otherwise, the new behavior will go into
> effect on 2020-11-23.
>
> Thanks!
> -Tikhon Jelvis, on behalf of the Haskell.org Committee
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From emilypi at cohomolo.gy  Sun Nov 15 18:45:41 2020
From: emilypi at cohomolo.gy (Emily Pillmore)
Date: Sun, 15 Nov 2020 18:45:41 +0000
Subject: [Haskell-cafe] [ANN] base64-bytestring-1.2.0.1 + future plans
Message-ID: <khjgt88v.ff207aa9-4e6b-45c0-b205-8b34cb3d6b1f@we.are.superhuman.com>

Hi Everyone,

I'm pleased to announce that we've released a new version of `base64-bytestring` that now supports `bytestring-0.11` in a backwards-compatible manner.

I'd also like to make an RFC: we are thinking that we will drop support for GHC versions <7.10 in future releases of the project. The earliest release  in which this can be expected will be around 6 months from now. The dev burden for supporting back to 7.0 is high, and unless someone screams in protest, the value does not seem to be there.

I'd like to get your thoughts on this.

Cheers,

Emily
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From oleg.grenrus at iki.fi  Sun Nov 15 18:48:18 2020
From: oleg.grenrus at iki.fi (Oleg Grenrus)
Date: Sun, 15 Nov 2020 20:48:18 +0200
Subject: [Haskell-cafe] Reading Haddock sources on hackage no longer
 possible with simple browsers?
In-Reply-To: <CAKH6PiVEJN1oKJ=U+VnkoE-gp0+dDwzh3f8sUymon+==no=mUw@mail.gmail.com>
References: <CAKH6PiVEJN1oKJ=U+VnkoE-gp0+dDwzh3f8sUymon+==no=mUw@mail.gmail.com>
Message-ID: <b57ec54d-dfab-2a50-5cfc-a8055974f32f@iki.fi>

About hiding some parts of the DOM tree with aria-hidden attribute.
https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/ARIA_Techniques/Using_the_aria-hidden_attribute

I'm :+1: to making accessibility-first designs / markup. We forgot that
completely when accepting new color scheme for haddock. The accessible
and pretty-looking are not in conflict, but not easy.

- Oleg

On 15.11.2020 17.19, M Douglas McIlroy wrote:
>> I am pretty sure nobody writes code like this
>> I confirmed your example, reading with lynx and w3m.
>> wouldn’t just directly opening the sources (in a text editor) be simpler? Is there a (simple) way to preserve the experience when browsing using Lynx without also holding back features aimed at a regular browsing experience?
> I second that.  I have always been annoyed by the ransom-note
> appearance of colorized  listings. But that's just my taste. I
> suspect, though, that lots of people have been frustrated when they
> discover they can't  use the code they see because it's festooned with
> markup. Golang.org offers similar listings, but also provides a button
> for selecting the underlying plain text. I would like hackage a lot
> better if it did so, too.
>
> Doug
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.

From sjcjoosten+haskell at gmail.com  Mon Nov 16 00:12:38 2020
From: sjcjoosten+haskell at gmail.com (Sebastiaan Joosten)
Date: Sun, 15 Nov 2020 19:12:38 -0500
Subject: [Haskell-cafe] Reading Haddock sources on hackage no longer
 possible with simple browsers?
In-Reply-To: <b57ec54d-dfab-2a50-5cfc-a8055974f32f@iki.fi>
References: <CAKH6PiVEJN1oKJ=U+VnkoE-gp0+dDwzh3f8sUymon+==no=mUw@mail.gmail.com>
 <b57ec54d-dfab-2a50-5cfc-a8055974f32f@iki.fi>
Message-ID: <CABhTcUtfZrRduyvK5xZ5oJY=ASZK9keRds3mqvkqpqZp5U5ydw@mail.gmail.com>

I'm all for accessibility-first, but Oleg's solution won't help. Here's a
test page for some features that are frequently discussed in this context:
https://sjcjoosten.nl/tmp/test.html

Opening this in a browser shows the following content:

This content is perceivable by all browsers but should not be copiable by
most.

The standard says this content should not be perceivable by screen readers.

This content is rendered via JavaScript and is not perceivable for those
without JavaScript
Here's what Lynx users see (line-wraps are due to the width of my terminal):
   This content is perceivable by all browsers but should not be copiable
   by most.

   The standard says this content should not be perceivable by screen
   readers.

   The standard says this content is not perceivable, following the HTML
   hidden tag.

   The standard says this content is not perceivable, using CSS.

There are separate issues that passed this thread:
- on Lynx, some things that are tooltips are displayed inline, they should
not be displayed at all
- using select+copy, some things are selected and copied (when I tried this
in Chrome, this only happens if I copy while my mouse is over the Show/Eq
element)
There is actually a third use-case to consider, namely brower+screenreader
combinations. Using apple's screen reader with Safari simply reads the
'should not be perceivable' line to me as well.

Johannes created an issue for this here:
https://github.com/haskell/haddock/issues/1250
I'll put my suggestions on how to fix this there.

Best,

Sebastiaan


On Sun, Nov 15, 2020 at 1:49 PM Oleg Grenrus <oleg.grenrus at iki.fi> wrote:

> About hiding some parts of the DOM tree with aria-hidden attribute.
>
> https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/ARIA_Techniques/Using_the_aria-hidden_attribute
>
> I'm :+1: to making accessibility-first designs / markup. We forgot that
> completely when accepting new color scheme for haddock. The accessible
> and pretty-looking are not in conflict, but not easy.
>
> - Oleg
>
> On 15.11.2020 17.19, M Douglas McIlroy wrote:
> >> I am pretty sure nobody writes code like this
> >> I confirmed your example, reading with lynx and w3m.
> >> wouldn’t just directly opening the sources (in a text editor) be
> simpler? Is there a (simple) way to preserve the experience when browsing
> using Lynx without also holding back features aimed at a regular browsing
> experience?
> > I second that.  I have always been annoyed by the ransom-note
> > appearance of colorized  listings. But that's just my taste. I
> > suspect, though, that lots of people have been frustrated when they
> > discover they can't  use the code they see because it's festooned with
> > markup. Golang.org offers similar listings, but also provides a button
> > for selecting the underlying plain text. I would like hackage a lot
> > better if it did so, too.
> >
> > Doug
> > _______________________________________________
> > Haskell-Cafe mailing list
> > To (un)subscribe, modify options or view archives go to:
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> > Only members subscribed via the mailman list are allowed to post.
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From carter.schonwald at gmail.com  Mon Nov 16 18:02:52 2020
From: carter.schonwald at gmail.com (Carter Schonwald)
Date: Mon, 16 Nov 2020 12:02:52 -0600
Subject: [Haskell-cafe] Psa : perhaps time for maintainers to start
	migrating off Travis ci
Message-ID: <CAHYVw0zCcXr2f6OyhH1acxuwqH0VcpSbqAtnX0iUNvp4F1bY5g@mail.gmail.com>

Hey everyone: it looks like, from my perspective and experiences, that
Travis ci should perhaps now be viewed as not open source friendly. Or even
converging on hostile?

1) crazy long queue times/ latency for oss ci actions to run

2) very low concurrency on oss builds.

3) very low build build  minute caps for oss that require high touch
customer support contact to adjust.

I’ve started moving my own projects slowly to gh actions for now, though
there’s also gitlab ci , src hut and other options that may suit different
folks.

There’s definitely some ways to keep on having the clever cabal caching we
know and love that folks like the Haskell-ci folks and others have hacked
out for Travis be available on other platforms, though I don’t think
there’s consolidated docs for those yet ?  Def seen it discussed though.

https://github.com/haskell-CI/haskell-ci/issues/411

Heres a url to my dupe ticket where I share an example naive use of the
setup Haskell gh actions Config, definitely not perfect. But kinda amazing
to have Mac and Linux and windows ci all in one ! :)
-------------- next part --------------
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From ulidtko at gmail.com  Mon Nov 16 18:15:46 2020
From: ulidtko at gmail.com (ulidtko at gmail.com)
Date: Mon, 16 Nov 2020 20:15:46 +0200
Subject: [Haskell-cafe]
 =?utf-8?q?Psa_=3A_perhaps_time_for_maintainers_to_?=
 =?utf-8?q?start_migrating_off_Travis_ci?=
In-Reply-To: <CAHYVw0zCcXr2f6OyhH1acxuwqH0VcpSbqAtnX0iUNvp4F1bY5g@mail.gmail.com>
References: <CAHYVw0zCcXr2f6OyhH1acxuwqH0VcpSbqAtnX0iUNvp4F1bY5g@mail.gmail.com>
Message-ID: <AQIWJQ.P0G2QUENB78M2@gmail.com>

Speaking of CI systems and OpenSource, I'd like to mention CircleCI as 
well: https://circleci.com/open-source/
(No affiliation, just a happy user.)

Did have slightly negative experience with TravisCI recently, can 
confirm the sentiment.

On Mon, Nov 16 2020 at 12:02:52 PM -0600, Carter Schonwald 
<carter.schonwald at gmail.com> wrote:
> Hey everyone: it looks like, from my perspective and experiences, 
> that Travis ci should perhaps now be viewed as not open source 
> friendly. Or even converging on hostile?
> 
> 1) crazy long queue times/ latency for oss ci actions to run
> 
> 2) very low concurrency on oss builds.
> 
> 3) very low build build  minute caps for oss that require high touch 
> customer support contact to adjust.
> 
> I’ve started moving my own projects slowly to gh actions for now, 
> though there’s also gitlab ci , src hut and other options that may 
> suit different folks.
> 
> There’s definitely some ways to keep on having the clever cabal 
> caching we know and love that folks like the Haskell-ci folks and 
> others have hacked out for Travis be available on other platforms, 
> though I don’t think there’s consolidated docs for those yet ?  
> Def seen it discussed though.
> 
> https://github.com/haskell-CI/haskell-ci/issues/411
> 
> Heres a url to my dupe ticket where I share an example naive use of 
> the setup Haskell gh actions Config, definitely not perfect. But 
> kinda amazing to have Mac and Linux and windows ci all in one ! :)
> 



From mihai.maruseac at gmail.com  Mon Nov 16 23:38:46 2020
From: mihai.maruseac at gmail.com (Mihai Maruseac)
Date: Mon, 16 Nov 2020 15:38:46 -0800
Subject: [Haskell-cafe] Psa : perhaps time for maintainers to start
 migrating off Travis ci
In-Reply-To: <AQIWJQ.P0G2QUENB78M2@gmail.com>
References: <CAHYVw0zCcXr2f6OyhH1acxuwqH0VcpSbqAtnX0iUNvp4F1bY5g@mail.gmail.com>
 <AQIWJQ.P0G2QUENB78M2@gmail.com>
Message-ID: <CAOMsUMLGL=7z2AphqxaDqcGScdULr0EcgW=gf9xz5KimOV85gw@mail.gmail.com>

As a user of all of the following, GitHub Actions > Circle CI > Travis.

You get much more control on Github Actions, you can cache stuff, you
can control when it runs.

On Mon, Nov 16, 2020 at 10:17 AM <ulidtko at gmail.com> wrote:
>
> Speaking of CI systems and OpenSource, I'd like to mention CircleCI as
> well: https://circleci.com/open-source/
> (No affiliation, just a happy user.)
>
> Did have slightly negative experience with TravisCI recently, can
> confirm the sentiment.
>
> On Mon, Nov 16 2020 at 12:02:52 PM -0600, Carter Schonwald
> <carter.schonwald at gmail.com> wrote:
> > Hey everyone: it looks like, from my perspective and experiences,
> > that Travis ci should perhaps now be viewed as not open source
> > friendly. Or even converging on hostile?
> >
> > 1) crazy long queue times/ latency for oss ci actions to run
> >
> > 2) very low concurrency on oss builds.
> >
> > 3) very low build build  minute caps for oss that require high touch
> > customer support contact to adjust.
> >
> > I’ve started moving my own projects slowly to gh actions for now,
> > though there’s also gitlab ci , src hut and other options that may
> > suit different folks.
> >
> > There’s definitely some ways to keep on having the clever cabal
> > caching we know and love that folks like the Haskell-ci folks and
> > others have hacked out for Travis be available on other platforms,
> > though I don’t think there’s consolidated docs for those yet ?
> > Def seen it discussed though.
> >
> > https://github.com/haskell-CI/haskell-ci/issues/411
> >
> > Heres a url to my dupe ticket where I share an example naive use of
> > the setup Haskell gh actions Config, definitely not perfect. But
> > kinda amazing to have Mac and Linux and windows ci all in one ! :)
> >
>
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.



-- 
Mihai Maruseac (MM)
"If you can't solve a problem, then there's an easier problem you can
solve: find it." -- George Polya

From carter.schonwald at gmail.com  Tue Nov 17 00:16:43 2020
From: carter.schonwald at gmail.com (Carter Schonwald)
Date: Mon, 16 Nov 2020 18:16:43 -0600
Subject: [Haskell-cafe] Psa : perhaps time for maintainers to start
 migrating off Travis ci
In-Reply-To: <CAOMsUMLGL=7z2AphqxaDqcGScdULr0EcgW=gf9xz5KimOV85gw@mail.gmail.com>
References: <CAHYVw0zCcXr2f6OyhH1acxuwqH0VcpSbqAtnX0iUNvp4F1bY5g@mail.gmail.com>
 <AQIWJQ.P0G2QUENB78M2@gmail.com>
 <CAOMsUMLGL=7z2AphqxaDqcGScdULr0EcgW=gf9xz5KimOV85gw@mail.gmail.com>
Message-ID: <CAHYVw0yZD3MT71aEDUp39TEgYLxYYe0Y0pa3NdxzHt2kLf0_Fw@mail.gmail.com>

this mirrors my current understanding of all the choices myself, and it
certainly helps that GH *explicitly* puts the OSS/free tier on equal or
footing with paid customers.
which  absolutely makes sense given their various corporate structures (GH
actions is a path to folks perhaps wanting to use azure services more
organically? )

On Mon, Nov 16, 2020 at 5:39 PM Mihai Maruseac <mihai.maruseac at gmail.com>
wrote:

> As a user of all of the following, GitHub Actions > Circle CI > Travis.
>
> You get much more control on Github Actions, you can cache stuff, you
> can control when it runs.
>
> On Mon, Nov 16, 2020 at 10:17 AM <ulidtko at gmail.com> wrote:
> >
> > Speaking of CI systems and OpenSource, I'd like to mention CircleCI as
> > well: https://circleci.com/open-source/
> > (No affiliation, just a happy user.)
> >
> > Did have slightly negative experience with TravisCI recently, can
> > confirm the sentiment.
> >
> > On Mon, Nov 16 2020 at 12:02:52 PM -0600, Carter Schonwald
> > <carter.schonwald at gmail.com> wrote:
> > > Hey everyone: it looks like, from my perspective and experiences,
> > > that Travis ci should perhaps now be viewed as not open source
> > > friendly. Or even converging on hostile?
> > >
> > > 1) crazy long queue times/ latency for oss ci actions to run
> > >
> > > 2) very low concurrency on oss builds.
> > >
> > > 3) very low build build  minute caps for oss that require high touch
> > > customer support contact to adjust.
> > >
> > > I’ve started moving my own projects slowly to gh actions for now,
> > > though there’s also gitlab ci , src hut and other options that may
> > > suit different folks.
> > >
> > > There’s definitely some ways to keep on having the clever cabal
> > > caching we know and love that folks like the Haskell-ci folks and
> > > others have hacked out for Travis be available on other platforms,
> > > though I don’t think there’s consolidated docs for those yet ?
> > > Def seen it discussed though.
> > >
> > > https://github.com/haskell-CI/haskell-ci/issues/411
> > >
> > > Heres a url to my dupe ticket where I share an example naive use of
> > > the setup Haskell gh actions Config, definitely not perfect. But
> > > kinda amazing to have Mac and Linux and windows ci all in one ! :)
> > >
> >
> >
> > _______________________________________________
> > Haskell-Cafe mailing list
> > To (un)subscribe, modify options or view archives go to:
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> > Only members subscribed via the mailman list are allowed to post.
>
>
>
> --
> Mihai Maruseac (MM)
> "If you can't solve a problem, then there's an easier problem you can
> solve: find it." -- George Polya
>
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From jo at durchholz.org  Tue Nov 17 06:18:59 2020
From: jo at durchholz.org (Joachim Durchholz)
Date: Tue, 17 Nov 2020 07:18:59 +0100
Subject: [Haskell-cafe] Psa : perhaps time for maintainers to start
 migrating off Travis ci
In-Reply-To: <CAHYVw0yZD3MT71aEDUp39TEgYLxYYe0Y0pa3NdxzHt2kLf0_Fw@mail.gmail.com>
References: <CAHYVw0zCcXr2f6OyhH1acxuwqH0VcpSbqAtnX0iUNvp4F1bY5g@mail.gmail.com>
 <AQIWJQ.P0G2QUENB78M2@gmail.com>
 <CAOMsUMLGL=7z2AphqxaDqcGScdULr0EcgW=gf9xz5KimOV85gw@mail.gmail.com>
 <CAHYVw0yZD3MT71aEDUp39TEgYLxYYe0Y0pa3NdxzHt2kLf0_Fw@mail.gmail.com>
Message-ID: <77986ff2-c8d4-25d3-3451-e23db4e4ea4b@durchholz.org>

Careful about Github.
It's currently OSS-friendly, but MS sometimes changes strategies 
abruptly, so they might move away from OSS, and much faster than Travis.
Plus the more of Github's features you use, the harder it will be to 
migrate away from them when that happens (harder than with Travis).

Maybe Gitlab is a viable alternative. At least the licensing is easier - 
the server code is MIT.
They do dual licensing (Community and Enterprise Edition), so they could 
become "too commercial" over time, but if/when that happens, there's 
always the MIT-licensed Community Edition that can be taken over by 
volunteers for development. (Which in turn makes going full commercial 
less attractive for them, so it's a bit of a self-inhibiting prophecy.)

(Disclaimer: I have no stake in the issue either way.)

Am 17.11.20 um 01:16 schrieb Carter Schonwald:
> this mirrors my current understanding of all the choices myself, and it 
> certainly helps that GH *explicitly* puts the OSS/free tier on equal or  
> footing with paid customers.
> which  absolutely makes sense given their various corporate structures 
> (GH actions is a path to folks perhaps wanting to use azure services 
> more organically? )
> 
> On Mon, Nov 16, 2020 at 5:39 PM Mihai Maruseac <mihai.maruseac at gmail.com 
> <mailto:mihai.maruseac at gmail.com>> wrote:
> 
>     As a user of all of the following, GitHub Actions > Circle CI > Travis.
> 
>     You get much more control on Github Actions, you can cache stuff, you
>     can control when it runs.
> 
>     On Mon, Nov 16, 2020 at 10:17 AM <ulidtko at gmail.com
>     <mailto:ulidtko at gmail.com>> wrote:
>      >
>      > Speaking of CI systems and OpenSource, I'd like to mention
>     CircleCI as
>      > well: https://circleci.com/open-source/
>      > (No affiliation, just a happy user.)
>      >
>      > Did have slightly negative experience with TravisCI recently, can
>      > confirm the sentiment.
>      >
>      > On Mon, Nov 16 2020 at 12:02:52 PM -0600, Carter Schonwald
>      > <carter.schonwald at gmail.com <mailto:carter.schonwald at gmail.com>>
>     wrote:
>      > > Hey everyone: it looks like, from my perspective and experiences,
>      > > that Travis ci should perhaps now be viewed as not open source
>      > > friendly. Or even converging on hostile?
>      > >
>      > > 1) crazy long queue times/ latency for oss ci actions to run
>      > >
>      > > 2) very low concurrency on oss builds.
>      > >
>      > > 3) very low build build  minute caps for oss that require high
>     touch
>      > > customer support contact to adjust.
>      > >
>      > > I’ve started moving my own projects slowly to gh actions for now,
>      > > though there’s also gitlab ci , src hut and other options that may
>      > > suit different folks.
>      > >
>      > > There’s definitely some ways to keep on having the clever cabal
>      > > caching we know and love that folks like the Haskell-ci folks and
>      > > others have hacked out for Travis be available on other platforms,
>      > > though I don’t think there’s consolidated docs for those yet ?
>      > > Def seen it discussed though.
>      > >
>      > > https://github.com/haskell-CI/haskell-ci/issues/411
>      > >
>      > > Heres a url to my dupe ticket where I share an example naive use of
>      > > the setup Haskell gh actions Config, definitely not perfect. But
>      > > kinda amazing to have Mac and Linux and windows ci all in one ! :)
>      > >
>      >
>      >
>      > _______________________________________________
>      > Haskell-Cafe mailing list
>      > To (un)subscribe, modify options or view archives go to:
>      > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>      > Only members subscribed via the mailman list are allowed to post.
> 
> 
> 
>     -- 
>     Mihai Maruseac (MM)
>     "If you can't solve a problem, then there's an easier problem you can
>     solve: find it." -- George Polya
> 
> 
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
> 


From b at chreekat.net  Tue Nov 17 06:54:34 2020
From: b at chreekat.net (Bryan Richter)
Date: Tue, 17 Nov 2020 08:54:34 +0200
Subject: [Haskell-cafe] Psa : perhaps time for maintainers to start
 migrating off Travis ci
In-Reply-To: <77986ff2-c8d4-25d3-3451-e23db4e4ea4b@durchholz.org>
References: <CAHYVw0zCcXr2f6OyhH1acxuwqH0VcpSbqAtnX0iUNvp4F1bY5g@mail.gmail.com>
 <AQIWJQ.P0G2QUENB78M2@gmail.com>
 <CAOMsUMLGL=7z2AphqxaDqcGScdULr0EcgW=gf9xz5KimOV85gw@mail.gmail.com>
 <CAHYVw0yZD3MT71aEDUp39TEgYLxYYe0Y0pa3NdxzHt2kLf0_Fw@mail.gmail.com>
 <77986ff2-c8d4-25d3-3451-e23db4e4ea4b@durchholz.org>
Message-ID: <CAH9BU=w1jkRO1iZX-y=b7E=yD7KEEZnb2kg7b1p6n6xtLAaKhw@mail.gmail.com>

I have to agree with Joachim. Everybody is good to OSS until it comes
time to tighten the belt. That time has just come earlier to TravisCI
than it has to Microsoft.

None of these organizations are beholden to the people who use their
services for free. Inversely, all of them ARE lawfully beholden to
their owners and their paying customers.

The viable long term strategies are (1) do it yourself [the blessing
and curse of OSS], or (2) become a paying customer!

On Tue, Nov 17, 2020 at 8:19 AM Joachim Durchholz <jo at durchholz.org> wrote:
>
> Careful about Github.
> It's currently OSS-friendly, but MS sometimes changes strategies
> abruptly, so they might move away from OSS, and much faster than Travis.
> Plus the more of Github's features you use, the harder it will be to
> migrate away from them when that happens (harder than with Travis).
>
> Maybe Gitlab is a viable alternative. At least the licensing is easier -
> the server code is MIT.
> They do dual licensing (Community and Enterprise Edition), so they could
> become "too commercial" over time, but if/when that happens, there's
> always the MIT-licensed Community Edition that can be taken over by
> volunteers for development. (Which in turn makes going full commercial
> less attractive for them, so it's a bit of a self-inhibiting prophecy.)
>
> (Disclaimer: I have no stake in the issue either way.)
>
> Am 17.11.20 um 01:16 schrieb Carter Schonwald:
> > this mirrors my current understanding of all the choices myself, and it
> > certainly helps that GH *explicitly* puts the OSS/free tier on equal or
> > footing with paid customers.
> > which  absolutely makes sense given their various corporate structures
> > (GH actions is a path to folks perhaps wanting to use azure services
> > more organically? )
> >
> > On Mon, Nov 16, 2020 at 5:39 PM Mihai Maruseac <mihai.maruseac at gmail.com
> > <mailto:mihai.maruseac at gmail.com>> wrote:
> >
> >     As a user of all of the following, GitHub Actions > Circle CI > Travis.
> >
> >     You get much more control on Github Actions, you can cache stuff, you
> >     can control when it runs.
> >
> >     On Mon, Nov 16, 2020 at 10:17 AM <ulidtko at gmail.com
> >     <mailto:ulidtko at gmail.com>> wrote:
> >      >
> >      > Speaking of CI systems and OpenSource, I'd like to mention
> >     CircleCI as
> >      > well: https://circleci.com/open-source/
> >      > (No affiliation, just a happy user.)
> >      >
> >      > Did have slightly negative experience with TravisCI recently, can
> >      > confirm the sentiment.
> >      >
> >      > On Mon, Nov 16 2020 at 12:02:52 PM -0600, Carter Schonwald
> >      > <carter.schonwald at gmail.com <mailto:carter.schonwald at gmail.com>>
> >     wrote:
> >      > > Hey everyone: it looks like, from my perspective and experiences,
> >      > > that Travis ci should perhaps now be viewed as not open source
> >      > > friendly. Or even converging on hostile?
> >      > >
> >      > > 1) crazy long queue times/ latency for oss ci actions to run
> >      > >
> >      > > 2) very low concurrency on oss builds.
> >      > >
> >      > > 3) very low build build  minute caps for oss that require high
> >     touch
> >      > > customer support contact to adjust.
> >      > >
> >      > > I’ve started moving my own projects slowly to gh actions for now,
> >      > > though there’s also gitlab ci , src hut and other options that may
> >      > > suit different folks.
> >      > >
> >      > > There’s definitely some ways to keep on having the clever cabal
> >      > > caching we know and love that folks like the Haskell-ci folks and
> >      > > others have hacked out for Travis be available on other platforms,
> >      > > though I don’t think there’s consolidated docs for those yet ?
> >      > > Def seen it discussed though.
> >      > >
> >      > > https://github.com/haskell-CI/haskell-ci/issues/411
> >      > >
> >      > > Heres a url to my dupe ticket where I share an example naive use of
> >      > > the setup Haskell gh actions Config, definitely not perfect. But
> >      > > kinda amazing to have Mac and Linux and windows ci all in one ! :)
> >      > >
> >      >
> >      >
> >      > _______________________________________________
> >      > Haskell-Cafe mailing list
> >      > To (un)subscribe, modify options or view archives go to:
> >      > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> >      > Only members subscribed via the mailman list are allowed to post.
> >
> >
> >
> >     --
> >     Mihai Maruseac (MM)
> >     "If you can't solve a problem, then there's an easier problem you can
> >     solve: find it." -- George Polya
> >
> >
> > _______________________________________________
> > Haskell-Cafe mailing list
> > To (un)subscribe, modify options or view archives go to:
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> > Only members subscribed via the mailman list are allowed to post.
> >
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.

From cma at bitemyapp.com  Tue Nov 17 11:26:33 2020
From: cma at bitemyapp.com (Christopher Allen)
Date: Tue, 17 Nov 2020 05:26:33 -0600
Subject: [Haskell-cafe] Psa : perhaps time for maintainers to start
	migrating off Travis ci
In-Reply-To: <CAH9BU=w1jkRO1iZX-y=b7E=yD7KEEZnb2kg7b1p6n6xtLAaKhw@mail.gmail.com>
References: <CAH9BU=w1jkRO1iZX-y=b7E=yD7KEEZnb2kg7b1p6n6xtLAaKhw@mail.gmail.com>
Message-ID: <69ED1EB5-EC88-47B0-9F37-653FB3314585@bitemyapp.com>

GitLab CI has been really nice in my work and personal projects. Easy to add your own worker to the free site too.

Sent from my iPhone

> On Nov 17, 2020, at 00:56, Bryan Richter <b at chreekat.net> wrote:
> 
> I have to agree with Joachim. Everybody is good to OSS until it comes
> time to tighten the belt. That time has just come earlier to TravisCI
> than it has to Microsoft.
> 
> None of these organizations are beholden to the people who use their
> services for free. Inversely, all of them ARE lawfully beholden to
> their owners and their paying customers.
> 
> The viable long term strategies are (1) do it yourself [the blessing
> and curse of OSS], or (2) become a paying customer!
> 
>> On Tue, Nov 17, 2020 at 8:19 AM Joachim Durchholz <jo at durchholz.org> wrote:
>> 
>> Careful about Github.
>> It's currently OSS-friendly, but MS sometimes changes strategies
>> abruptly, so they might move away from OSS, and much faster than Travis.
>> Plus the more of Github's features you use, the harder it will be to
>> migrate away from them when that happens (harder than with Travis).
>> 
>> Maybe Gitlab is a viable alternative. At least the licensing is easier -
>> the server code is MIT.
>> They do dual licensing (Community and Enterprise Edition), so they could
>> become "too commercial" over time, but if/when that happens, there's
>> always the MIT-licensed Community Edition that can be taken over by
>> volunteers for development. (Which in turn makes going full commercial
>> less attractive for them, so it's a bit of a self-inhibiting prophecy.)
>> 
>> (Disclaimer: I have no stake in the issue either way.)
>> 
>>> Am 17.11.20 um 01:16 schrieb Carter Schonwald:
>>> this mirrors my current understanding of all the choices myself, and it
>>> certainly helps that GH *explicitly* puts the OSS/free tier on equal or
>>> footing with paid customers.
>>> which  absolutely makes sense given their various corporate structures
>>> (GH actions is a path to folks perhaps wanting to use azure services
>>> more organically? )
>>> 
>>> On Mon, Nov 16, 2020 at 5:39 PM Mihai Maruseac <mihai.maruseac at gmail.com
>>> <mailto:mihai.maruseac at gmail.com>> wrote:
>>> 
>>>    As a user of all of the following, GitHub Actions > Circle CI > Travis.
>>> 
>>>    You get much more control on Github Actions, you can cache stuff, you
>>>    can control when it runs.
>>> 
>>>    On Mon, Nov 16, 2020 at 10:17 AM <ulidtko at gmail.com
>>>    <mailto:ulidtko at gmail.com>> wrote:
>>>> 
>>>> Speaking of CI systems and OpenSource, I'd like to mention
>>>    CircleCI as
>>>> well: https://circleci.com/open-source/
>>>> (No affiliation, just a happy user.)
>>>> 
>>>> Did have slightly negative experience with TravisCI recently, can
>>>> confirm the sentiment.
>>>> 
>>>> On Mon, Nov 16 2020 at 12:02:52 PM -0600, Carter Schonwald
>>>> <carter.schonwald at gmail.com <mailto:carter.schonwald at gmail.com>>
>>>    wrote:
>>>>> Hey everyone: it looks like, from my perspective and experiences,
>>>>> that Travis ci should perhaps now be viewed as not open source
>>>>> friendly. Or even converging on hostile?
>>>>> 
>>>>> 1) crazy long queue times/ latency for oss ci actions to run
>>>>> 
>>>>> 2) very low concurrency on oss builds.
>>>>> 
>>>>> 3) very low build build  minute caps for oss that require high
>>>    touch
>>>>> customer support contact to adjust.
>>>>> 
>>>>> I’ve started moving my own projects slowly to gh actions for now,
>>>>> though there’s also gitlab ci , src hut and other options that may
>>>>> suit different folks.
>>>>> 
>>>>> There’s definitely some ways to keep on having the clever cabal
>>>>> caching we know and love that folks like the Haskell-ci folks and
>>>>> others have hacked out for Travis be available on other platforms,
>>>>> though I don’t think there’s consolidated docs for those yet ?
>>>>> Def seen it discussed though.
>>>>> 
>>>>> https://github.com/haskell-CI/haskell-ci/issues/411
>>>>> 
>>>>> Heres a url to my dupe ticket where I share an example naive use of
>>>>> the setup Haskell gh actions Config, definitely not perfect. But
>>>>> kinda amazing to have Mac and Linux and windows ci all in one ! :)
>>>>> 
>>>> 
>>>> 
>>>> _______________________________________________
>>>> Haskell-Cafe mailing list
>>>> To (un)subscribe, modify options or view archives go to:
>>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>>>> Only members subscribed via the mailman list are allowed to post.
>>> 
>>> 
>>> 
>>>    --
>>>    Mihai Maruseac (MM)
>>>    "If you can't solve a problem, then there's an easier problem you can
>>>    solve: find it." -- George Polya
>>> 
>>> 
>>> _______________________________________________
>>> Haskell-Cafe mailing list
>>> To (un)subscribe, modify options or view archives go to:
>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>>> Only members subscribed via the mailman list are allowed to post.
>>> 
>> 
>> _______________________________________________
>> Haskell-Cafe mailing list
>> To (un)subscribe, modify options or view archives go to:
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>> Only members subscribed via the mailman list are allowed to post.
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.

From sumitraja at gmail.com  Tue Nov 17 12:20:10 2020
From: sumitraja at gmail.com (Sumit Raja)
Date: Tue, 17 Nov 2020 23:20:10 +1100
Subject: [Haskell-cafe] GHC linker error 8.8.4 Windows
Message-ID: <CAD4nrSfVYaqj+2d+h9yOyo6YUiE-zmr-t8afnB3fsvdEXzRCPQ@mail.gmail.com>

Hi,

Suddenly started getting the following linker error after I moved code
around in my project. It only seems to occur when I am building one
specific cabal test target. When building a dependent build it build
successfully but cabal repl test-xxx  fails. I have no consistent way to
repro but I will keep trying and file a defect..

GHCi, version 8.8.4: https://www.haskell.org/ghc/  :? for help
GHC runtime linker: fatal error: I found a duplicate definition for symbol
   __gmpn_sec_sqr_itch
whilst processing object file
   C:\Users\sumit\Apps\ghc-8.8.4\mingw\lib\libgmp.dll.a
The symbol was previously defined in

 C:\Users\sumit\Apps\ghc-8.8.4\lib\integer-gmp-1.0.2.0\HSinteger-gmp-1.0.2.0.o
This could be caused by:
   * Loading two different object files which export the same symbol
   * Specifying the same object file twice on the GHCi command line
   * An incorrect `package.conf' entry, causing some object to be
     loaded twice.
ghc.exe: panic! (the 'impossible' happened)
  (GHC version 8.8.4 for x86_64-unknown-mingw32):
        loadArchive
"C:\\Users\\sumit\\Apps\\ghc-8.8.4\\mingw\\lib\\libgmp.dll.a": failed

Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug

CallStack (from HasCallStack):
  die', called at .\\Distribution\\Client\\ProjectOrchestration.hs:1041:55
in main:Distribution.Client.ProjectOrchestration
cabal.exe: repl failed for mkr-txn-0.1.0.0-inplace-test-mkr-txn.

Regards
Sumit
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From sylvain at haskus.fr  Tue Nov 17 13:41:34 2020
From: sylvain at haskus.fr (Sylvain Henry)
Date: Tue, 17 Nov 2020 14:41:34 +0100
Subject: [Haskell-cafe] GHC linker error 8.8.4 Windows
In-Reply-To: <CAD4nrSfVYaqj+2d+h9yOyo6YUiE-zmr-t8afnB3fsvdEXzRCPQ@mail.gmail.com>
References: <CAD4nrSfVYaqj+2d+h9yOyo6YUiE-zmr-t8afnB3fsvdEXzRCPQ@mail.gmail.com>
Message-ID: <b57071a1-2a9b-2a9c-1eeb-748dbfa336b1@haskus.fr>

Hi,

On Windows, GHC embeds GMP (the C library) directly into the integer-gmp 
package. So you mustn't try to link against another libgmp library to 
avoid duplicated symbol errors (as the one you've got).

It may be that you have a dependency of this specific test (or the test 
itself) that has the following stanza in its Cabal file: 
"extra-libraries: gmp"

Regards,
Sylvain


On 17/11/2020 13:20, Sumit Raja wrote:
> Hi,
>
> Suddenly started getting the following linker error after I moved code 
> around in my project. It only seems to occur when I am building one 
> specific cabal test target. When building a dependent build it build 
> successfully but cabal repl test-xxx fails. I have no consistent way 
> to repro but I will keep trying and file a defect..
>
> GHCi, version 8.8.4: https://www.haskell.org/ghc/  :? for help
> GHC runtime linker: fatal error: I found a duplicate definition for symbol
>    __gmpn_sec_sqr_itch
> whilst processing object file
>    C:\Users\sumit\Apps\ghc-8.8.4\mingw\lib\libgmp.dll.a
> The symbol was previously defined in
>  C:\Users\sumit\Apps\ghc-8.8.4\lib\integer-gmp-1.0.2.0\HSinteger-gmp-1.0.2.0.o
> This could be caused by:
>    * Loading two different object files which export the same symbol
>    * Specifying the same object file twice on the GHCi command line
>    * An incorrect `package.conf' entry, causing some object to be
>      loaded twice.
> ghc.exe: panic! (the 'impossible' happened)
>   (GHC version 8.8.4 for x86_64-unknown-mingw32):
>         loadArchive 
> "C:\\Users\\sumit\\Apps\\ghc-8.8.4\\mingw\\lib\\libgmp.dll.a": failed
>
> Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug
>
> CallStack (from HasCallStack):
>   die', called at 
> .\\Distribution\\Client\\ProjectOrchestration.hs:1041:55 in 
> main:Distribution.Client.ProjectOrchestration
> cabal.exe: repl failed for mkr-txn-0.1.0.0-inplace-test-mkr-txn.
>
> Regards
> Sumit
>
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From amindfv at mailbox.org  Tue Nov 17 23:54:58 2020
From: amindfv at mailbox.org (amindfv at mailbox.org)
Date: Tue, 17 Nov 2020 18:54:58 -0500
Subject: [Haskell-cafe] Why is my 'text' missing an instance?
Message-ID: <20201117235458.GA9101@painter.painter>

tl;dr: I seem to have two versions of 'text' on my system, both of which should have an instance for (Binary Text). However, one version seems to claim not to have that instance.

    $ cat test.hs
    import qualified Data.Text as T
    import qualified Data.Binary as B
    
    main = print $ B.encode $ T.pack "hello"
    
    $ /usr/local/bin/ghci --version
    The Glorious Glasgow Haskell Compilation System, version 8.10.2
    
    $ /usr/local/bin/ghci test.hs
    GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
    [1 of 1] Compiling Main             ( test.hs, interpreted )
    
    test.hs:4:16: error:
        • No instance for (B.Binary T.Text)
            arising from a use of ‘B.encode’
        • In the second argument of ‘($)’, namely
            ‘B.encode $ T.pack "hello"’
          In the expression: print $ B.encode $ T.pack "hello"
          In an equation for ‘main’: main = print $ B.encode $ T.pack "hello"
      |
    4 | main = print $ B.encode $ T.pack "hello"
      |                ^^^^^^^^^^^^^^^^^^^^^^^^^
    Failed, no modules loaded.
    
    $ /usr/local/bin/ghc-pkg list text
    /usr/local/lib/ghc-8.10.2/package.conf.d
        text-1.2.3.2
    /home/name/.ghc/x86_64-linux-8.10.2/package.conf.d
        text-1.2.4.1

    $ ghc-pkg-8.10.2 list text
    [same result]

    $ /usr/local/bin/ghci -package text-1.2.3.2 test.hs
    GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
    [1 of 1] Compiling Main             ( test.hs, interpreted )
    Ok, one module loaded.

    $ /usr/local/bin/ghci -package text-1.2.4.1 test.hs
    GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
    [1 of 1] Compiling Main             ( test.hs, interpreted )
    
    test.hs:4:16: error:
        • No instance for (B.Binary T.Text)
            arising from a use of ‘B.encode’
        • In the second argument of ‘($)’, namely
            ‘B.encode $ T.pack "hello"’
          In the expression: print $ B.encode $ T.pack "hello"
          In an equation for ‘main’: main = print $ B.encode $ T.pack "hello"
      |
    4 | main = print $ B.encode $ T.pack "hello"
      |                ^^^^^^^^^^^^^^^^^^^^^^^^^
    Failed, no modules loaded.

Both text-1.2.3.2 and text-1.2.4.1 have a Binary instance for Text. What's going on?

(After writing this out I rebuilt an unmodified clone of text-1.2.4.1 but I see the same results.)

Thanks,
Tom


From tikhon at jelv.is  Wed Nov 18 00:14:13 2020
From: tikhon at jelv.is (Tikhon Jelvis)
Date: Tue, 17 Nov 2020 16:14:13 -0800
Subject: [Haskell-cafe] Why is my 'text' missing an instance?
In-Reply-To: <20201117235458.GA9101@painter.painter>
References: <20201117235458.GA9101@painter.painter>
Message-ID: <CAJN5CVLQ0+9sop057VF1FVWSsYqW4SZvOnvD7EOMLB-0zj7QCg@mail.gmail.com>

Wild guess—could there be an inconsistency between the version of the
binary package the text library was built against and the version you got
the class from in your failing example?

I don't see how that would happen given your setup, but it's also the only
way I can imagine seeing that particular error.

On Tue, Nov 17, 2020, 15:57 amindfv--- via Haskell-Cafe <
haskell-cafe at haskell.org> wrote:

> tl;dr: I seem to have two versions of 'text' on my system, both of which
> should have an instance for (Binary Text). However, one version seems to
> claim not to have that instance.
>
>     $ cat test.hs
>     import qualified Data.Text as T
>     import qualified Data.Binary as B
>
>     main = print $ B.encode $ T.pack "hello"
>
>     $ /usr/local/bin/ghci --version
>     The Glorious Glasgow Haskell Compilation System, version 8.10.2
>
>     $ /usr/local/bin/ghci test.hs
>     GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
>     [1 of 1] Compiling Main             ( test.hs, interpreted )
>
>     test.hs:4:16: error:
>         • No instance for (B.Binary T.Text)
>             arising from a use of ‘B.encode’
>         • In the second argument of ‘($)’, namely
>             ‘B.encode $ T.pack "hello"’
>           In the expression: print $ B.encode $ T.pack "hello"
>           In an equation for ‘main’: main = print $ B.encode $ T.pack
> "hello"
>       |
>     4 | main = print $ B.encode $ T.pack "hello"
>       |                ^^^^^^^^^^^^^^^^^^^^^^^^^
>     Failed, no modules loaded.
>
>     $ /usr/local/bin/ghc-pkg list text
>     /usr/local/lib/ghc-8.10.2/package.conf.d
>         text-1.2.3.2
>     /home/name/.ghc/x86_64-linux-8.10.2/package.conf.d
>         text-1.2.4.1
>
>     $ ghc-pkg-8.10.2 list text
>     [same result]
>
>     $ /usr/local/bin/ghci -package text-1.2.3.2 test.hs
>     GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
>     [1 of 1] Compiling Main             ( test.hs, interpreted )
>     Ok, one module loaded.
>
>     $ /usr/local/bin/ghci -package text-1.2.4.1 test.hs
>     GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
>     [1 of 1] Compiling Main             ( test.hs, interpreted )
>
>     test.hs:4:16: error:
>         • No instance for (B.Binary T.Text)
>             arising from a use of ‘B.encode’
>         • In the second argument of ‘($)’, namely
>             ‘B.encode $ T.pack "hello"’
>           In the expression: print $ B.encode $ T.pack "hello"
>           In an equation for ‘main’: main = print $ B.encode $ T.pack
> "hello"
>       |
>     4 | main = print $ B.encode $ T.pack "hello"
>       |                ^^^^^^^^^^^^^^^^^^^^^^^^^
>     Failed, no modules loaded.
>
> Both text-1.2.3.2 and text-1.2.4.1 have a Binary instance for Text. What's
> going on?
>
> (After writing this out I rebuilt an unmodified clone of text-1.2.4.1 but
> I see the same results.)
>
> Thanks,
> Tom
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From ietf-dane at dukhovni.org  Wed Nov 18 00:19:05 2020
From: ietf-dane at dukhovni.org (Viktor Dukhovni)
Date: Tue, 17 Nov 2020 19:19:05 -0500
Subject: [Haskell-cafe] Why is my 'text' missing an instance?
In-Reply-To: <20201117235458.GA9101@painter.painter>
References: <20201117235458.GA9101@painter.painter>
Message-ID: <20201118001905.GS1464@straasha.imrryr.org>

On Tue, Nov 17, 2020 at 06:54:58PM -0500, amindfv--- via Haskell-Cafe wrote:

> tl;dr: I seem to have two versions of 'text' on my system, both of
> which should have an instance for (Binary Text). However, one version
> seems to claim not to have that instance.
> 
>     $ /usr/local/bin/ghci -package text-1.2.4.1 test.hs
>     GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
>     [1 of 1] Compiling Main             ( test.hs, interpreted )
>     
>     test.hs:4:16: error:
>         • No instance for (B.Binary T.Text)
>             arising from a use of ‘B.encode’

Hard to say what's different on your system, but on a Fedora 31 system
with GHC 8.10.2 and text-1.2.4.1, I'm unable to reproduce the symptoms
you report.

    $ ghci -package text-1.2.4.1
    GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
    Prelude> import qualified Data.Text as T
    Prelude T> import qualified Data.Binary as B
    Prelude T B> main = print $ B.encode $ T.pack "hello"
    Prelude T B> main
    "\NUL\NUL\NUL\NUL\NUL\NUL\NUL\ENQhello"

The interface file for Text 1.2.4.1 has the expected instances:

    $ ghc-pkg list
    ~/.local/ghc-8.10/lib/ghc-8.10.2/lib/package.conf.d
        ...
        text-1.2.4.1
        ...
    ~/.ghc/x86_64-linux-8.10.2/package.conf.d
        (no packages)

    $ ghc --show-iface ~/.local/ghc-8.10/lib/ghc-8.10.2/lib/x86_64-linux-ghc-8.10.2/text-1.2.4.1/Data/Text.hi | grep '^instance'
    instance [orphan] Data.Binary.Class.Binary [Data.Text.Internal.Text]
    instance [orphan] Data.Data.Data [Data.Text.Internal.Text]
    instance [orphan] GHC.Classes.Eq [Data.Text.Internal.Text]
    instance [orphan] GHC.Exts.IsList [Data.Text.Internal.Text]
    instance [orphan] Data.String.IsString [Data.Text.Internal.Text]
    instance [orphan] Language.Haskell.TH.Syntax.Lift [GHC.Types.LiftedRep,
    instance [orphan] GHC.Base.Monoid [Data.Text.Internal.Text]
    instance [orphan] Control.DeepSeq.NFData [Data.Text.Internal.Text]
    instance [orphan] GHC.Classes.Ord [Data.Text.Internal.Text]
    instance [orphan] Text.Printf.PrintfArg [Data.Text.Internal.Text]
    instance [orphan] GHC.Read.Read [Data.Text.Internal.Text]
    instance [orphan] GHC.Base.Semigroup [Data.Text.Internal.Text]

-- 
    Viktor.

From allbery.b at gmail.com  Wed Nov 18 01:01:38 2020
From: allbery.b at gmail.com (Brandon Allbery)
Date: Tue, 17 Nov 2020 20:01:38 -0500
Subject: [Haskell-cafe] Why is my 'text' missing an instance?
In-Reply-To: <CAJN5CVLQ0+9sop057VF1FVWSsYqW4SZvOnvD7EOMLB-0zj7QCg@mail.gmail.com>
References: <20201117235458.GA9101@painter.painter>
 <CAJN5CVLQ0+9sop057VF1FVWSsYqW4SZvOnvD7EOMLB-0zj7QCg@mail.gmail.com>
Message-ID: <CAKFCL4VesdLvn1Mwa1P8HCWYPV-1=ykUJk-WL5SAnQcvNMHhZw@mail.gmail.com>

Actually that can happen if there are two versions of text built against
different versions of binary, but ghc (or cabal in old mode, which let ghc
do it) picked the wrong version of binary for the version of text it chose.

On Tue, Nov 17, 2020, 19:15 Tikhon Jelvis <tikhon at jelv.is> wrote:

> Wild guess—could there be an inconsistency between the version of the
> binary package the text library was built against and the version you got
> the class from in your failing example?
>
> I don't see how that would happen given your setup, but it's also the only
> way I can imagine seeing that particular error.
>
> On Tue, Nov 17, 2020, 15:57 amindfv--- via Haskell-Cafe <
> haskell-cafe at haskell.org> wrote:
>
>> tl;dr: I seem to have two versions of 'text' on my system, both of which
>> should have an instance for (Binary Text). However, one version seems to
>> claim not to have that instance.
>>
>>     $ cat test.hs
>>     import qualified Data.Text as T
>>     import qualified Data.Binary as B
>>
>>     main = print $ B.encode $ T.pack "hello"
>>
>>     $ /usr/local/bin/ghci --version
>>     The Glorious Glasgow Haskell Compilation System, version 8.10.2
>>
>>     $ /usr/local/bin/ghci test.hs
>>     GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
>>     [1 of 1] Compiling Main             ( test.hs, interpreted )
>>
>>     test.hs:4:16: error:
>>         • No instance for (B.Binary T.Text)
>>             arising from a use of ‘B.encode’
>>         • In the second argument of ‘($)’, namely
>>             ‘B.encode $ T.pack "hello"’
>>           In the expression: print $ B.encode $ T.pack "hello"
>>           In an equation for ‘main’: main = print $ B.encode $ T.pack
>> "hello"
>>       |
>>     4 | main = print $ B.encode $ T.pack "hello"
>>       |                ^^^^^^^^^^^^^^^^^^^^^^^^^
>>     Failed, no modules loaded.
>>
>>     $ /usr/local/bin/ghc-pkg list text
>>     /usr/local/lib/ghc-8.10.2/package.conf.d
>>         text-1.2.3.2
>>     /home/name/.ghc/x86_64-linux-8.10.2/package.conf.d
>>         text-1.2.4.1
>>
>>     $ ghc-pkg-8.10.2 list text
>>     [same result]
>>
>>     $ /usr/local/bin/ghci -package text-1.2.3.2 test.hs
>>     GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
>>     [1 of 1] Compiling Main             ( test.hs, interpreted )
>>     Ok, one module loaded.
>>
>>     $ /usr/local/bin/ghci -package text-1.2.4.1 test.hs
>>     GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
>>     [1 of 1] Compiling Main             ( test.hs, interpreted )
>>
>>     test.hs:4:16: error:
>>         • No instance for (B.Binary T.Text)
>>             arising from a use of ‘B.encode’
>>         • In the second argument of ‘($)’, namely
>>             ‘B.encode $ T.pack "hello"’
>>           In the expression: print $ B.encode $ T.pack "hello"
>>           In an equation for ‘main’: main = print $ B.encode $ T.pack
>> "hello"
>>       |
>>     4 | main = print $ B.encode $ T.pack "hello"
>>       |                ^^^^^^^^^^^^^^^^^^^^^^^^^
>>     Failed, no modules loaded.
>>
>> Both text-1.2.3.2 and text-1.2.4.1 have a Binary instance for Text.
>> What's going on?
>>
>> (After writing this out I rebuilt an unmodified clone of text-1.2.4.1 but
>> I see the same results.)
>>
>> Thanks,
>> Tom
>>
>> _______________________________________________
>> Haskell-Cafe mailing list
>> To (un)subscribe, modify options or view archives go to:
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>> Only members subscribed via the mailman list are allowed to post.
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From amindfv at mailbox.org  Wed Nov 18 03:45:45 2020
From: amindfv at mailbox.org (amindfv at mailbox.org)
Date: Tue, 17 Nov 2020 22:45:45 -0500
Subject: [Haskell-cafe] Why is my 'text' missing an instance?
In-Reply-To: <CAJN5CVLQ0+9sop057VF1FVWSsYqW4SZvOnvD7EOMLB-0zj7QCg@mail.gmail.com>
References: <20201117235458.GA9101@painter.painter>
 <CAJN5CVLQ0+9sop057VF1FVWSsYqW4SZvOnvD7EOMLB-0zj7QCg@mail.gmail.com>
Message-ID: <20201118034545.GA5231@painter.painter>

Aha - this was it, mystery solved!

I was thrown off the scent by "instance Binary Text" not showing up in the instance list when doing this in ghci:

    > :m + Data.Text
    > :m + Data.Binary
    > :i Text

Thank you!
Tom

On Tue, Nov 17, 2020 at 04:14:13PM -0800, Tikhon Jelvis wrote:
> Wild guess—could there be an inconsistency between the version of the
> binary package the text library was built against and the version you got
> the class from in your failing example?
> 
> I don't see how that would happen given your setup, but it's also the only
> way I can imagine seeing that particular error.
> 
> On Tue, Nov 17, 2020, 15:57 amindfv--- via Haskell-Cafe <
> haskell-cafe at haskell.org> wrote:
> 
> > tl;dr: I seem to have two versions of 'text' on my system, both of which
> > should have an instance for (Binary Text). However, one version seems to
> > claim not to have that instance.
> >
> >     $ cat test.hs
> >     import qualified Data.Text as T
> >     import qualified Data.Binary as B
> >
> >     main = print $ B.encode $ T.pack "hello"
> >
> >     $ /usr/local/bin/ghci --version
> >     The Glorious Glasgow Haskell Compilation System, version 8.10.2
> >
> >     $ /usr/local/bin/ghci test.hs
> >     GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
> >     [1 of 1] Compiling Main             ( test.hs, interpreted )
> >
> >     test.hs:4:16: error:
> >         • No instance for (B.Binary T.Text)
> >             arising from a use of ‘B.encode’
> >         • In the second argument of ‘($)’, namely
> >             ‘B.encode $ T.pack "hello"’
> >           In the expression: print $ B.encode $ T.pack "hello"
> >           In an equation for ‘main’: main = print $ B.encode $ T.pack
> > "hello"
> >       |
> >     4 | main = print $ B.encode $ T.pack "hello"
> >       |                ^^^^^^^^^^^^^^^^^^^^^^^^^
> >     Failed, no modules loaded.
> >
> >     $ /usr/local/bin/ghc-pkg list text
> >     /usr/local/lib/ghc-8.10.2/package.conf.d
> >         text-1.2.3.2
> >     /home/name/.ghc/x86_64-linux-8.10.2/package.conf.d
> >         text-1.2.4.1
> >
> >     $ ghc-pkg-8.10.2 list text
> >     [same result]
> >
> >     $ /usr/local/bin/ghci -package text-1.2.3.2 test.hs
> >     GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
> >     [1 of 1] Compiling Main             ( test.hs, interpreted )
> >     Ok, one module loaded.
> >
> >     $ /usr/local/bin/ghci -package text-1.2.4.1 test.hs
> >     GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
> >     [1 of 1] Compiling Main             ( test.hs, interpreted )
> >
> >     test.hs:4:16: error:
> >         • No instance for (B.Binary T.Text)
> >             arising from a use of ‘B.encode’
> >         • In the second argument of ‘($)’, namely
> >             ‘B.encode $ T.pack "hello"’
> >           In the expression: print $ B.encode $ T.pack "hello"
> >           In an equation for ‘main’: main = print $ B.encode $ T.pack
> > "hello"
> >       |
> >     4 | main = print $ B.encode $ T.pack "hello"
> >       |                ^^^^^^^^^^^^^^^^^^^^^^^^^
> >     Failed, no modules loaded.
> >
> > Both text-1.2.3.2 and text-1.2.4.1 have a Binary instance for Text. What's
> > going on?
> >
> > (After writing this out I rebuilt an unmodified clone of text-1.2.4.1 but
> > I see the same results.)
> >
> > Thanks,
> > Tom
> >
> > _______________________________________________
> > Haskell-Cafe mailing list
> > To (un)subscribe, modify options or view archives go to:
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> > Only members subscribed via the mailman list are allowed to post.

From immanuel.litzroth at gmail.com  Wed Nov 18 12:19:28 2020
From: immanuel.litzroth at gmail.com (Immanuel Litzroth)
Date: Wed, 18 Nov 2020 13:19:28 +0100
Subject: [Haskell-cafe] ghci module re exporting qualified as
Message-ID: <CAM1nAcyTimOMgXXP4KM0YZjT5k0j9oJww-8cxPX0zkvUDP=jKQ@mail.gmail.com>

I'm trying to make a test module to run tests.
I want to import the test functionality + imported functionality in
the scope of the test module under ghci.
I also want to have short names in the  Test module for reexported
modules. I am using Data.Map and Data.Set ... so lot's of conflicting
exports.
Is this possible?


#+BEGIN_SRC haskell :tangle T1.hs
module T1 (
   module Data.Map) where
import qualified Data.Map
#+END_SRC

works but no browsing info shows up
#+BEGIN_EXAMPLE
λ⊢ :show modules
T1  ....
λ⊢ :show imports
import T1 -- added automatically
import Prelude -- implicit
λ⊢ fromList []

<interactive>:114:1-8: error:
    Variable not in scope: fromList ∷ [a0] → t
λ⊢ Data.Map.fromList []
fromList []
λ⊢ :browse! T1

λ⊢
#+END_EXAMPLE


#+BEGIN_SRC haskell :tangle T2.hs
module T2 (
   module Map) where
import qualified Data.Map as Map
#+END_SRC

#+BEGIN_EXAMPLE
λ⊢ :show modules
T2
:show imports
import T2 -- added automatically
import Prelude -- implicit
λ⊢ fromList []

<interactive>:119:1-8: error:
    Variable not in scope: fromList ∷ [a0] → t
λ⊢ Map.fromList []

<interactive>:120:1-12: error:
    Not in scope: ‘Map.fromList’
    No module named ‘Map’ is imported.
λ⊢ Data.Map.fromList []
fromList []
λ⊢ :browse! T2

λ⊢
#+END_EXAMPLE


-- 
-- Researching the dual problem of finding the function that has a
given point as fixpoint.

From lemming at henning-thielemann.de  Wed Nov 18 15:14:53 2020
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed, 18 Nov 2020 16:14:53 +0100 (CET)
Subject: [Haskell-cafe] ghci module re exporting qualified as
In-Reply-To: <CAM1nAcyTimOMgXXP4KM0YZjT5k0j9oJww-8cxPX0zkvUDP=jKQ@mail.gmail.com>
References: <CAM1nAcyTimOMgXXP4KM0YZjT5k0j9oJww-8cxPX0zkvUDP=jKQ@mail.gmail.com>
Message-ID: <alpine.DEB.2.20.2011181614350.5716@sputnik>


On Wed, 18 Nov 2020, Immanuel Litzroth wrote:

> I'm trying to make a test module to run tests.
> I want to import the test functionality + imported functionality in
> the scope of the test module under ghci.
> I also want to have short names in the  Test module for reexported
> modules. I am using Data.Map and Data.Set ... so lot's of conflicting
> exports.
> Is this possible?
>
>
> #+BEGIN_SRC haskell :tangle T1.hs
> module T1 (
>   module Data.Map) where
> import qualified Data.Map
> #+END_SRC

Maybe omit the export list?

From immanuel.litzroth at gmail.com  Wed Nov 18 16:27:58 2020
From: immanuel.litzroth at gmail.com (Immanuel Litzroth)
Date: Wed, 18 Nov 2020 17:27:58 +0100
Subject: [Haskell-cafe] ghci module re exporting qualified as
In-Reply-To: <alpine.DEB.2.20.2011181614350.5716@sputnik>
References: <CAM1nAcyTimOMgXXP4KM0YZjT5k0j9oJww-8cxPX0zkvUDP=jKQ@mail.gmail.com>
 <alpine.DEB.2.20.2011181614350.5716@sputnik>
Message-ID: <CAM1nAcwypYEpy2FYdXq6o4FLThLjNQUOHi7Gst1so26AMzsMEg@mail.gmail.com>

You mean this?
#+BEGIN_SRC haskell :tangle T1.hs
module T1 where
import Data.Map as Map
#+END_SRC

that doesn't seem to do it:
#+BEGIN_EXAMPLE
λ⊢ :show modules
T1
λ⊢ :show imports
import T1 -- added automatically
import Prelude -- implicit
λ⊢ fromList

<interactive>:143:1-8: error: Variable not in scope: fromList
λ⊢ Map.fromList

<interactive>:144:1-12: error:
    Not in scope: ‘Map.fromList’
    No module named ‘Map’ is imported.
λ⊢ Data.Map.FromList

<interactive>:145:1-17: error:
    Not in scope: data constructor ‘Data.Map.FromList’
    No module named ‘Data.Map’ is imported.
λ⊢
#+END_EXAMPLE

On Wed, Nov 18, 2020 at 4:14 PM Henning Thielemann
<lemming at henning-thielemann.de> wrote:
>
>
> On Wed, 18 Nov 2020, Immanuel Litzroth wrote:
>
> > I'm trying to make a test module to run tests.
> > I want to import the test functionality + imported functionality in
> > the scope of the test module under ghci.
> > I also want to have short names in the  Test module for reexported
> > modules. I am using Data.Map and Data.Set ... so lot's of conflicting
> > exports.
> > Is this possible?
> >
> >
> > #+BEGIN_SRC haskell :tangle T1.hs
> > module T1 (
> >   module Data.Map) where
> > import qualified Data.Map
> > #+END_SRC
>
> Maybe omit the export list?



-- 
-- Researching the dual problem of finding the function that has a
given point as fixpoint.

From lemming at henning-thielemann.de  Wed Nov 18 16:30:51 2020
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed, 18 Nov 2020 17:30:51 +0100 (CET)
Subject: [Haskell-cafe] ghci module re exporting qualified as
In-Reply-To: <CAM1nAcwypYEpy2FYdXq6o4FLThLjNQUOHi7Gst1so26AMzsMEg@mail.gmail.com>
References: <CAM1nAcyTimOMgXXP4KM0YZjT5k0j9oJww-8cxPX0zkvUDP=jKQ@mail.gmail.com>
 <alpine.DEB.2.20.2011181614350.5716@sputnik>
 <CAM1nAcwypYEpy2FYdXq6o4FLThLjNQUOHi7Gst1so26AMzsMEg@mail.gmail.com>
Message-ID: <alpine.DEB.2.20.2011181730140.5716@sputnik>


On Wed, 18 Nov 2020, Immanuel Litzroth wrote:

> You mean this?
> #+BEGIN_SRC haskell :tangle T1.hs
> module T1 where
> import Data.Map as Map
> #+END_SRC
>
> that doesn't seem to do it:
> #+BEGIN_EXAMPLE
> λ⊢ :show modules
> T1
> λ⊢ :show imports
> import T1 -- added automatically
> import Prelude -- implicit
> λ⊢ fromList
>
> <interactive>:143:1-8: error: Variable not in scope: fromList
> λ⊢ Map.fromList
>
> <interactive>:144:1-12: error:
>    Not in scope: ‘Map.fromList’
>    No module named ‘Map’ is imported.
> λ⊢ Data.Map.FromList


Hm. Was the module compiled? You can only benefit from imports, if the 
module is interpreted.

From allbery.b at gmail.com  Wed Nov 18 16:42:40 2020
From: allbery.b at gmail.com (Brandon Allbery)
Date: Wed, 18 Nov 2020 11:42:40 -0500
Subject: [Haskell-cafe] ghci module re exporting qualified as
In-Reply-To: <alpine.DEB.2.20.2011181730140.5716@sputnik>
References: <CAM1nAcyTimOMgXXP4KM0YZjT5k0j9oJww-8cxPX0zkvUDP=jKQ@mail.gmail.com>
 <alpine.DEB.2.20.2011181614350.5716@sputnik>
 <CAM1nAcwypYEpy2FYdXq6o4FLThLjNQUOHi7Gst1so26AMzsMEg@mail.gmail.com>
 <alpine.DEB.2.20.2011181730140.5716@sputnik>
Message-ID: <CAKFCL4VYnBh-7swv-sVG_5gnvcvSmOEWraYwNd_SBtRjnWLjBQ@mail.gmail.com>

I'm under the impression that they want to export names qualified, but
qualification only happens on import. If you export names from an imported
module, they will appear to be from the imported module, not the original.

On Wed, Nov 18, 2020, 11:32 Henning Thielemann <
lemming at henning-thielemann.de> wrote:

>
> On Wed, 18 Nov 2020, Immanuel Litzroth wrote:
>
> > You mean this?
> > #+BEGIN_SRC haskell :tangle T1.hs
> > module T1 where
> > import Data.Map as Map
> > #+END_SRC
> >
> > that doesn't seem to do it:
> > #+BEGIN_EXAMPLE
> > λ⊢ :show modules
> > T1
> > λ⊢ :show imports
> > import T1 -- added automatically
> > import Prelude -- implicit
> > λ⊢ fromList
> >
> > <interactive>:143:1-8: error: Variable not in scope: fromList
> > λ⊢ Map.fromList
> >
> > <interactive>:144:1-12: error:
> >    Not in scope: ‘Map.fromList’
> >    No module named ‘Map’ is imported.
> > λ⊢ Data.Map.FromList
>
>
> Hm. Was the module compiled? You can only benefit from imports, if the
> module is interpreted._______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From lemming at henning-thielemann.de  Wed Nov 18 16:44:56 2020
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed, 18 Nov 2020 17:44:56 +0100 (CET)
Subject: [Haskell-cafe] ghci module re exporting qualified as
In-Reply-To: <CAKFCL4VYnBh-7swv-sVG_5gnvcvSmOEWraYwNd_SBtRjnWLjBQ@mail.gmail.com>
References: <CAM1nAcyTimOMgXXP4KM0YZjT5k0j9oJww-8cxPX0zkvUDP=jKQ@mail.gmail.com>
 <alpine.DEB.2.20.2011181614350.5716@sputnik>
 <CAM1nAcwypYEpy2FYdXq6o4FLThLjNQUOHi7Gst1so26AMzsMEg@mail.gmail.com>
 <alpine.DEB.2.20.2011181730140.5716@sputnik>
 <CAKFCL4VYnBh-7swv-sVG_5gnvcvSmOEWraYwNd_SBtRjnWLjBQ@mail.gmail.com>
Message-ID: <alpine.DEB.2.20.2011181744030.5716@sputnik>


On Wed, 18 Nov 2020, Brandon Allbery wrote:

> I'm under the impression that they want to export names qualified, but 
> qualification only happens on import. If you export names from an 
> imported module, they will appear to be from the imported module, not 
> the original.

That's true for compiled Haskell. But I know I have already re-used the 
qualifications within interpreted modules in GHCi.

From aeroboy94 at gmail.com  Wed Nov 18 18:23:21 2020
From: aeroboy94 at gmail.com (Arian van Putten)
Date: Wed, 18 Nov 2020 19:23:21 +0100
Subject: [Haskell-cafe] Psa : perhaps time for maintainers to start
 migrating off Travis ci
In-Reply-To: <CAHYVw0zCcXr2f6OyhH1acxuwqH0VcpSbqAtnX0iUNvp4F1bY5g@mail.gmail.com>
References: <CAHYVw0zCcXr2f6OyhH1acxuwqH0VcpSbqAtnX0iUNvp4F1bY5g@mail.gmail.com>
Message-ID: <CADTZ2ECDqL2BrX7t68Az=0gt1_vw5AHR-tXfGB7Qf=1F51V1Jw@mail.gmail.com>

Thanks for the example Carter.

I've been struggling with Servant's CI since the recent Travis changes as
CI now somtimes takes up to multiple hours to complete.

It would be awesome if somebody would volunteer adding a Github or Gitlab
backend to haskell-ci; such that I do not have to re-invent the entire CI
systems that is in place currently from scratch though.  Killer feature for
us is the parsing of `Tested-With` in cabal files to adjust the build
matrix; as e.g. not all our packages for on GHCJS for example.

However  your example doesn't look that complicated. I'm going to play
around with it.

On Mon, Nov 16, 2020 at 7:04 PM Carter Schonwald <carter.schonwald at gmail.com>
wrote:

> Hey everyone: it looks like, from my perspective and experiences, that
> Travis ci should perhaps now be viewed as not open source friendly. Or even
> converging on hostile?
>
> 1) crazy long queue times/ latency for oss ci actions to run
>
> 2) very low concurrency on oss builds.
>
> 3) very low build build  minute caps for oss that require high touch
> customer support contact to adjust.
>
> I’ve started moving my own projects slowly to gh actions for now, though
> there’s also gitlab ci , src hut and other options that may suit different
> folks.
>
> There’s definitely some ways to keep on having the clever cabal caching we
> know and love that folks like the Haskell-ci folks and others have hacked
> out for Travis be available on other platforms, though I don’t think
> there’s consolidated docs for those yet ?  Def seen it discussed though.
>
> https://github.com/haskell-CI/haskell-ci/issues/411
>
> Heres a url to my dupe ticket where I share an example naive use of the
> setup Haskell gh actions Config, definitely not perfect. But kinda amazing
> to have Mac and Linux and windows ci all in one ! :)
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.



-- 
Groetjes,

Arian
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From sumitraja at gmail.com  Thu Nov 19 00:48:32 2020
From: sumitraja at gmail.com (Sumit Raja)
Date: Thu, 19 Nov 2020 11:48:32 +1100
Subject: [Haskell-cafe] Haskell-Cafe Digest, Vol 207, Issue 16
In-Reply-To: <mailman.1.1605700801.20950.haskell-cafe@haskell.org>
References: <mailman.1.1605700801.20950.haskell-cafe@haskell.org>
Message-ID: <CAD4nrSfKD940QzFO22hcseGBdq7fzjmQwMBEVspGr0Qw7u1S0g@mail.gmail.com>

> It may be that you have a dependency of this specific test (or the test
> itself) that has the following stanza in its Cabal file:
> "extra-libraries: gmp"
>
>
Thanks, makes sense. Any shortcuts to try and find which package has gmp
enabled?

Interestingly this problem doesn't happen with ghc-8.6.5. Does build order
decide on if this issue is triggered or not?

-Sumit
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From jo at durchholz.org  Thu Nov 19 07:12:13 2020
From: jo at durchholz.org (Joachim Durchholz)
Date: Thu, 19 Nov 2020 08:12:13 +0100
Subject: [Haskell-cafe] Psa : perhaps time for maintainers to start
 migrating off Travis ci
In-Reply-To: <CADTZ2ECDqL2BrX7t68Az=0gt1_vw5AHR-tXfGB7Qf=1F51V1Jw@mail.gmail.com>
References: <CAHYVw0zCcXr2f6OyhH1acxuwqH0VcpSbqAtnX0iUNvp4F1bY5g@mail.gmail.com>
 <CADTZ2ECDqL2BrX7t68Az=0gt1_vw5AHR-tXfGB7Qf=1F51V1Jw@mail.gmail.com>
Message-ID: <79ff1bb4-063e-deff-2b46-f94871a86d93@durchholz.org>

Am 18.11.20 um 19:23 schrieb Arian van Putten:
> It would be awesome if somebody would volunteer adding a Github or 
> Gitlab backend to haskell-ci;

What would be needed?

> such that I do not have to re-invent the entire CI systems that is
> in place currently from scratch though Killer feature for us is the 
> parsing of `Tested-With` in cabal files to adjust the build matrix; 
> as e.g. not all our packages for on GHCJS for example.
I.e. volunteers would need to know (or learn) what's there currently.

Other question: What kind of hardware would be needed?
I.e. how much CPU/RAM to get the queues emptied quickly enough.

Regards,
Jo

(Disclaimer: I cannot volunteer due to lack of time, just trying to 
contribute whatever tooling ops knowledge I happen to have.)

From sylvain at haskus.fr  Thu Nov 19 10:38:36 2020
From: sylvain at haskus.fr (Sylvain Henry)
Date: Thu, 19 Nov 2020 11:38:36 +0100
Subject: [Haskell-cafe] Haskell-Cafe Digest, Vol 207, Issue 16
In-Reply-To: <CAD4nrSfKD940QzFO22hcseGBdq7fzjmQwMBEVspGr0Qw7u1S0g@mail.gmail.com>
References: <mailman.1.1605700801.20950.haskell-cafe@haskell.org>
 <CAD4nrSfKD940QzFO22hcseGBdq7fzjmQwMBEVspGr0Qw7u1S0g@mail.gmail.com>
Message-ID: <c9f70408-ac1a-f949-a6de-d30710c4d065@haskus.fr>

On 19/11/2020 01:48, Sumit Raja wrote:
>
>     It may be that you have a dependency of this specific test (or the
>     test
>     itself) that has the following stanza in its Cabal file:
>     "extra-libraries: gmp"
>
>
> Thanks, makes sense. Any shortcuts to try and find which package has 
> gmp enabled?
>
You may grep for "gmp" in your "package.conf.d". A usual suspect is 
"bitvec" which has a "libmp" flag that you can disable.

> Interestingly this problem doesn't happen with ghc-8.6.5. Does build 
> order decide on if this issue is triggered or not?
>
I don't think so. My guess would be that using 8.6.5 changes the build 
plan (e.g. earlier versions of "bitvec" didn't explicitly link with gmp).

Cheers,
Sylvain

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From carter.schonwald at gmail.com  Thu Nov 19 20:40:39 2020
From: carter.schonwald at gmail.com (Carter Schonwald)
Date: Thu, 19 Nov 2020 14:40:39 -0600
Subject: [Haskell-cafe] Psa : perhaps time for maintainers to start
 migrating off Travis ci
In-Reply-To: <CADTZ2ECDqL2BrX7t68Az=0gt1_vw5AHR-tXfGB7Qf=1F51V1Jw@mail.gmail.com>
References: <CAHYVw0zCcXr2f6OyhH1acxuwqH0VcpSbqAtnX0iUNvp4F1bY5g@mail.gmail.com>
 <CADTZ2ECDqL2BrX7t68Az=0gt1_vw5AHR-tXfGB7Qf=1F51V1Jw@mail.gmail.com>
Message-ID: <CAHYVw0xNZLBdhxiRJ4me3EvsEqAACWmfbKALqXKE=BMbug5s_g@mail.gmail.com>

I've gotten things to be even nice and working on windows finally!
(including having the steps shared on on platforms in a single buildway :)
! )

plus figuring out how to sidestep a fun / terrible issue on windows , but
now fixed for me :)

https://github.com/cartazio/ralist/actions/runs/373071421/workflow  is the
current one i have and attached is a copy that should be easy to adapt

enjoy!

On Wed, Nov 18, 2020 at 12:23 PM Arian van Putten <aeroboy94 at gmail.com>
wrote:

> Thanks for the example Carter.
>
> I've been struggling with Servant's CI since the recent Travis changes as
> CI now somtimes takes up to multiple hours to complete.
>
> It would be awesome if somebody would volunteer adding a Github or Gitlab
> backend to haskell-ci; such that I do not have to re-invent the entire CI
> systems that is in place currently from scratch though.  Killer feature for
> us is the parsing of `Tested-With` in cabal files to adjust the build
> matrix; as e.g. not all our packages for on GHCJS for example.
>
> However  your example doesn't look that complicated. I'm going to play
> around with it.
>
> On Mon, Nov 16, 2020 at 7:04 PM Carter Schonwald <
> carter.schonwald at gmail.com> wrote:
>
>> Hey everyone: it looks like, from my perspective and experiences, that
>> Travis ci should perhaps now be viewed as not open source friendly. Or even
>> converging on hostile?
>>
>> 1) crazy long queue times/ latency for oss ci actions to run
>>
>> 2) very low concurrency on oss builds.
>>
>> 3) very low build build  minute caps for oss that require high touch
>> customer support contact to adjust.
>>
>> I’ve started moving my own projects slowly to gh actions for now, though
>> there’s also gitlab ci , src hut and other options that may suit different
>> folks.
>>
>> There’s definitely some ways to keep on having the clever cabal caching
>> we know and love that folks like the Haskell-ci folks and others have
>> hacked out for Travis be available on other platforms, though I don’t think
>> there’s consolidated docs for those yet ?  Def seen it discussed though.
>>
>> https://github.com/haskell-CI/haskell-ci/issues/411
>>
>> Heres a url to my dupe ticket where I share an example naive use of the
>> setup Haskell gh actions Config, definitely not perfect. But kinda amazing
>> to have Mac and Linux and windows ci all in one ! :)
>>
>> _______________________________________________
>> Haskell-Cafe mailing list
>> To (un)subscribe, modify options or view archives go to:
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>> Only members subscribed via the mailman list are allowed to post.
>
>
>
> --
> Groetjes,
>
> Arian
>
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From karel.gardas at centrum.cz  Fri Nov 20 18:23:16 2020
From: karel.gardas at centrum.cz (Karel Gardas)
Date: Fri, 20 Nov 2020 19:23:16 +0100
Subject: [Haskell-cafe] xmonad: eyes based navigation between monitors.
Message-ID: <742633a6-bdee-1a32-de7f-bb2ebc5f1f14@centrum.cz>


Hello,

I'm using xmonad in a setup with 3 monitors and I'm curious if anybody
here got kind of eyes-based navigation working between monitors/workspaces.

Explanation: I need to type into windows on different monitors but in
not specific order. Sometime I got too deep into thinking that I forget
to switch workspace and then I type to different window in different
workspace than is intended (and which I see with eyes). Basically I'd
like some mode where xmonad will switch workspaces based on my eye/head
position so only workspace I follow with eyes will be active.

I see that such software (following head/eyes) already exist in AI
domain (E.g. NV's xavier NX developer kit demo: from 16:00:
https://www.youtube.com/watch?v=aUz1bNGm04w) but I'm more interested in
amd64/linux setup as this is for my workstation...

Any idea highly appreciated!

Thanks!
Karel

From johnz at pleasantnightmare.com  Fri Nov 20 19:09:14 2020
From: johnz at pleasantnightmare.com (John Z.)
Date: Fri, 20 Nov 2020 14:09:14 -0500
Subject: [Haskell-cafe] xmonad: eyes based navigation between monitors.
In-Reply-To: <742633a6-bdee-1a32-de7f-bb2ebc5f1f14@centrum.cz>
References: <742633a6-bdee-1a32-de7f-bb2ebc5f1f14@centrum.cz>
Message-ID: <X7gUWiuaQgGDzkxX@johnslap.localdomain>

Don't have a ready solution, but this is such an interesting idea since I
have same setup. I might try a toy weekend project using a random kinect
I have lying around.


> Hello,
> 
> I'm using xmonad in a setup with 3 monitors and I'm curious if anybody
> here got kind of eyes-based navigation working between monitors/workspaces.
> 
> Explanation: I need to type into windows on different monitors but in
> not specific order. Sometime I got too deep into thinking that I forget
> to switch workspace and then I type to different window in different
> workspace than is intended (and which I see with eyes). Basically I'd
> like some mode where xmonad will switch workspaces based on my eye/head
> position so only workspace I follow with eyes will be active.
> 
> I see that such software (following head/eyes) already exist in AI
> domain (E.g. NV's xavier NX developer kit demo: from 16:00:
> https://www.youtube.com/watch?v=aUz1bNGm04w) but I'm more interested in
> amd64/linux setup as this is for my workstation...
> 
> Any idea highly appreciated!
> 
> Thanks!
> Karel
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.

-- 
John Z.
"Its too bad she won't live... but then again, who does?"

From ivanperezdominguez at gmail.com  Fri Nov 20 20:20:55 2020
From: ivanperezdominguez at gmail.com (Ivan Perez)
Date: Fri, 20 Nov 2020 15:20:55 -0500
Subject: [Haskell-cafe] xmonad: eyes based navigation between monitors.
In-Reply-To: <X7gUWiuaQgGDzkxX@johnslap.localdomain>
References: <742633a6-bdee-1a32-de7f-bb2ebc5f1f14@centrum.cz>
 <X7gUWiuaQgGDzkxX@johnslap.localdomain>
Message-ID: <CACZKWEKWyvvfbEgT11vPjeN_8CZ85F_+EahoQ8RzA=d6O6Pibg@mail.gmail.com>

Hi all

In case it's useful, the following two projects I built a few years ago
might help:

Kinect control for the game Haskanoid:

https://github.com/ivanperez-keera/haskanoid/blob/develop/src/Input.hs#L237-L280

Webcam-based face position/distance detection module for a posture monitor:

https://github.com/keera-studios/keera-posture/blob/develop/src/AI/CV/PostureProcessors.hs#L40

Either method could achieve something like what you want. I'd recommend
playing with having the kinect/webcam in different positions (not just
between the monitors, and potentially even slightly to the right of the
rightmost monitor, or to the left of the leftmost one).

I never managed to make eye detection work on Kinect. I heard the very
latest version of the kinect (under development in 2017) was able to detect
eye movement well, but never tried it myself. It would have been a cool
accessibility feature for haskanoid.

All the best,

Ivan

On Fri, 20 Nov 2020 at 14:10, John Z. <johnz at pleasantnightmare.com> wrote:

> Don't have a ready solution, but this is such an interesting idea since I
> have same setup. I might try a toy weekend project using a random kinect
> I have lying around.
>
>
> > Hello,
> >
> > I'm using xmonad in a setup with 3 monitors and I'm curious if anybody
> > here got kind of eyes-based navigation working between
> monitors/workspaces.
> >
> > Explanation: I need to type into windows on different monitors but in
> > not specific order. Sometime I got too deep into thinking that I forget
> > to switch workspace and then I type to different window in different
> > workspace than is intended (and which I see with eyes). Basically I'd
> > like some mode where xmonad will switch workspaces based on my eye/head
> > position so only workspace I follow with eyes will be active.
> >
> > I see that such software (following head/eyes) already exist in AI
> > domain (E.g. NV's xavier NX developer kit demo: from 16:00:
> > https://www.youtube.com/watch?v=aUz1bNGm04w) but I'm more interested in
> > amd64/linux setup as this is for my workstation...
> >
> > Any idea highly appreciated!
> >
> > Thanks!
> > Karel
> > _______________________________________________
> > Haskell-Cafe mailing list
> > To (un)subscribe, modify options or view archives go to:
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> > Only members subscribed via the mailman list are allowed to post.
>
> --
> John Z.
> "Its too bad she won't live... but then again, who does?"
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From tikhon at jelv.is  Fri Nov 20 20:40:51 2020
From: tikhon at jelv.is (Tikhon Jelvis)
Date: Fri, 20 Nov 2020 12:40:51 -0800
Subject: [Haskell-cafe] xmonad: eyes based navigation between monitors.
In-Reply-To: <CACZKWEKWyvvfbEgT11vPjeN_8CZ85F_+EahoQ8RzA=d6O6Pibg@mail.gmail.com>
References: <742633a6-bdee-1a32-de7f-bb2ebc5f1f14@centrum.cz>
 <X7gUWiuaQgGDzkxX@johnslap.localdomain>
 <CACZKWEKWyvvfbEgT11vPjeN_8CZ85F_+EahoQ8RzA=d6O6Pibg@mail.gmail.com>
Message-ID: <CAJN5CVL0ziLuTw01j1wo8emVHf7ROWEQTSpovzV9wNJYqvu6WQ@mail.gmail.com>

I've thought about this myself, although not seriously. At one point, I
even considered buying a monitor with eye-tracking built in :).

There's a commercial eye-tracking product from Tobii aimed at gamers, and
my instinct is that starting from a purpose-built eye-tracker would work
much better than using a webcam or Kinect. However, it seems the Tobii
product is fundamentally limited to one monitor at a time and only has
unofficial Linux support.

If you do make something work, I'd love to hear about it.

On Fri, Nov 20, 2020, 12:24 Ivan Perez <ivanperezdominguez at gmail.com> wrote:

> Hi all
>
> In case it's useful, the following two projects I built a few years ago
> might help:
>
> Kinect control for the game Haskanoid:
>
>
> https://github.com/ivanperez-keera/haskanoid/blob/develop/src/Input.hs#L237-L280
>
> Webcam-based face position/distance detection module for a posture monitor:
>
>
> https://github.com/keera-studios/keera-posture/blob/develop/src/AI/CV/PostureProcessors.hs#L40
>
> Either method could achieve something like what you want. I'd recommend
> playing with having the kinect/webcam in different positions (not just
> between the monitors, and potentially even slightly to the right of the
> rightmost monitor, or to the left of the leftmost one).
>
> I never managed to make eye detection work on Kinect. I heard the very
> latest version of the kinect (under development in 2017) was able to detect
> eye movement well, but never tried it myself. It would have been a cool
> accessibility feature for haskanoid.
>
> All the best,
>
> Ivan
>
> On Fri, 20 Nov 2020 at 14:10, John Z. <johnz at pleasantnightmare.com> wrote:
>
>> Don't have a ready solution, but this is such an interesting idea since I
>> have same setup. I might try a toy weekend project using a random kinect
>> I have lying around.
>>
>>
>> > Hello,
>> >
>> > I'm using xmonad in a setup with 3 monitors and I'm curious if anybody
>> > here got kind of eyes-based navigation working between
>> monitors/workspaces.
>> >
>> > Explanation: I need to type into windows on different monitors but in
>> > not specific order. Sometime I got too deep into thinking that I forget
>> > to switch workspace and then I type to different window in different
>> > workspace than is intended (and which I see with eyes). Basically I'd
>> > like some mode where xmonad will switch workspaces based on my eye/head
>> > position so only workspace I follow with eyes will be active.
>> >
>> > I see that such software (following head/eyes) already exist in AI
>> > domain (E.g. NV's xavier NX developer kit demo: from 16:00:
>> > https://www.youtube.com/watch?v=aUz1bNGm04w) but I'm more interested in
>> > amd64/linux setup as this is for my workstation...
>> >
>> > Any idea highly appreciated!
>> >
>> > Thanks!
>> > Karel
>> > _______________________________________________
>> > Haskell-Cafe mailing list
>> > To (un)subscribe, modify options or view archives go to:
>> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>> > Only members subscribed via the mailman list are allowed to post.
>>
>> --
>> John Z.
>> "Its too bad she won't live... but then again, who does?"
>> _______________________________________________
>> Haskell-Cafe mailing list
>> To (un)subscribe, modify options or view archives go to:
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>> Only members subscribed via the mailman list are allowed to post.
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From leah at vuxu.org  Mon Nov 23 10:59:01 2020
From: leah at vuxu.org (Leah Neukirchen)
Date: Mon, 23 Nov 2020 11:59:01 +0100
Subject: [Haskell-cafe] Virtual Munich Haskell Meeting, 2020-11-25 @ 19:30
Message-ID: <875z5wqqyy.fsf@vuxu.org>

Dear all,

This week, our monthly Munich Haskell Meeting will take place again on
Wednesday, November 25 at 19:30.

**Due to meetup limitations in Bavaria, this meeting will take place online!**

For details see here:

https://muenchen.haskell.bayern/dates.html

Everybody is welcome, especially the Haskellers from Bavaria that do
not usually come to our Munich meetings due to travel distance!

cu,
-- 
Leah Neukirchen  <leah at vuxu.org>  https://leahneukirchen.org/

From johannes.waldmann at htwk-leipzig.de  Mon Nov 23 13:53:05 2020
From: johannes.waldmann at htwk-leipzig.de (Johannes Waldmann)
Date: Mon, 23 Nov 2020 14:53:05 +0100
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
Message-ID: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>

Dear Cafe -

you might find this entertaining:
an error in my code that cost me some hours
(most Pictures are equal?)  until I finally realized

 instance Eq a => Eq (Picture a) where
   p == q = dim p == dim q
-    && all (\ i -> contents p i == contents q i) (bounds p)
+    && all (\ i -> contents p i == contents q i) (A.range $ bounds p)

Henning already called this "Matlab league" behaviour,
https://mail.haskell.org/pipermail/libraries/2016-February/026678.html

Well it's just a fun observation now, I am not implying anything. Enjoy!

- J.

Link to full source:
https://gitlab.imn.htwk-leipzig.de/autotool/all0/-/issues/660#note_24567

From svenpanne at gmail.com  Mon Nov 23 14:23:29 2020
From: svenpanne at gmail.com (Sven Panne)
Date: Mon, 23 Nov 2020 15:23:29 +0100
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
Message-ID: <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>

Am Mo., 23. Nov. 2020 um 14:54 Uhr schrieb Johannes Waldmann <
johannes.waldmann at htwk-leipzig.de>:

> [...] Henning already called this "Matlab league" behaviour,
> https://mail.haskell.org/pipermail/libraries/2016-February/026678.html
>
> Well it's just a fun observation now, I am not implying anything. Enjoy!
>

There was a mega-thread in March/April 2017 about adding even more of this
nonsense... :-D
https://mail.haskell.org/pipermail/libraries/2017-March/027824.html Luckily
enough, there was no consensus.
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From manuel.schnecki at gmail.com  Mon Nov 23 15:00:42 2020
From: manuel.schnecki at gmail.com (Manuel Schneckenreither)
Date: Mon, 23 Nov 2020 16:00:42 +0100
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 (Sven Panne's message of "Mon, 23 Nov 2020 15:23:29 +0100")
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
Message-ID: <874klg6rtx.fsf@uibk.ac.at>


    >>>>> "SP" == Sven Panne <svenpanne at gmail.com> writes:

    SP> Am Mo., 23. Nov. 2020 um 14:54 Uhr schrieb Johannes Waldmann
    SP> <johannes.waldmann at htwk-leipzig.de>: [...] Henning already
    SP> called this "Matlab league" behaviour,
    SP> https://mail.haskell.org/pipermail/libraries/2016-February/026678.html

What is the intiutive way of implementing the tuple instance like this [1]

    instance Foldable ((,) a) where
      ..
      length _ = 1
      ..

I cannot come up with a real argument, except to say there is something.
For instance for Either, Left returns 0, and Right 1. But that there is
something isn't that already implied by the tuple? And even if that
would be the argument, the ⊥-case is not considered as the argument is
not evaluated.


[1] https://hackage.haskell.org/package/base-4.14.0.0/docs/src/Data.Foldable.html#line-363

From lemming at henning-thielemann.de  Mon Nov 23 15:09:40 2020
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Mon, 23 Nov 2020 16:09:40 +0100 (CET)
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <874klg6rtx.fsf@uibk.ac.at>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at>
Message-ID: <alpine.DEB.2.20.2011231608030.5933@sputnik>


On Mon, 23 Nov 2020, Manuel Schneckenreither wrote:

>    >>>>> "SP" == Sven Panne <svenpanne at gmail.com> writes:
>
>    SP> Am Mo., 23. Nov. 2020 um 14:54 Uhr schrieb Johannes Waldmann
>    SP> <johannes.waldmann at htwk-leipzig.de>: [...] Henning already
>    SP> called this "Matlab league" behaviour,
>    SP> https://mail.haskell.org/pipermail/libraries/2016-February/026678.html
>
> What is the intiutive way of implementing the tuple instance like this [1]
>
>    instance Foldable ((,) a) where
>      ..
>      length _ = 1
>      ..
>
> I cannot come up with a real argument, except to say there is something.

"length (a,b) == 1" is only a consequence of defining instance Foldable 
for pairs. It was not the argument to implement that instance, at all.

From manuel.schnecki at gmail.com  Mon Nov 23 15:21:13 2020
From: manuel.schnecki at gmail.com (Manuel Schneckenreither)
Date: Mon, 23 Nov 2020 16:21:13 +0100
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <alpine.DEB.2.20.2011231608030.5933@sputnik> (Henning
 Thielemann's message of "Mon, 23 Nov 2020 16:09:40 +0100 (CET)")
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at> <alpine.DEB.2.20.2011231608030.5933@sputnik>
Message-ID: <87wnyc5cba.fsf@gmail.com>

    >>>>> "HT" == Henning Thielemann <lemming at henning-thielemann.de> writes:

    HT> "length (a,b) == 1" is only a consequence of defining instance
    HT> Foldable for pairs. It was not the argument to implement that
    HT> instance, at all.

What was the argument to use 1, not 2 for instance? 

From david.feuer at gmail.com  Mon Nov 23 15:24:10 2020
From: david.feuer at gmail.com (David Feuer)
Date: Mon, 23 Nov 2020 10:24:10 -0500
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <87wnyc5cba.fsf@gmail.com>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at> <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
Message-ID: <CAMgWh9t2YF8XQeVWyqmxW0UhOF47LaX8pzVjdC_9TbTMfrRbsA@mail.gmail.com>

The expectation that length = getSum . foldMap (Sum . const 1)

On Mon, Nov 23, 2020, 10:21 AM Manuel Schneckenreither <
manuel.schnecki at gmail.com> wrote:

>     >>>>> "HT" == Henning Thielemann <lemming at henning-thielemann.de>
> writes:
>
>     HT> "length (a,b) == 1" is only a consequence of defining instance
>     HT> Foldable for pairs. It was not the argument to implement that
>     HT> instance, at all.
>
> What was the argument to use 1, not 2 for instance?
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From sjcjoosten+haskell at gmail.com  Mon Nov 23 15:30:51 2020
From: sjcjoosten+haskell at gmail.com (Sebastiaan Joosten)
Date: Mon, 23 Nov 2020 10:30:51 -0500
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <87wnyc5cba.fsf@gmail.com>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at> <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
Message-ID: <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>

length is part of the Foldable class:

length = foldl'
<https://hackage.haskell.org/package/base-4.14.0.0/docs/src/Data.Foldable.html#foldl%27>
(\c
<https://hackage.haskell.org/package/base-4.14.0.0/docs/src/Data.Foldable.html#local-6989586621679508859>
_ -> c
<https://hackage.haskell.org/package/base-4.14.0.0/docs/src/Data.Foldable.html#local-6989586621679508859>
+
<https://hackage.haskell.org/package/base-4.14.0.0/docs/src/GHC.Num.html#%2B>
1) 0
It is probably defined this way s.t. it satisfies:
length = length . toList
Not the actual definition, but you can read toList as:
toList = foldr (:) []

So as soon as one defines foldr for pairs:

foldr <https://hackage.haskell.org/package/base-4.14.0.0/docs/src/Data.Foldable.html#local-6989586621679508613>
f <https://hackage.haskell.org/package/base-4.14.0.0/docs/src/Data.Foldable.html#local-6989586621679508612>
z <https://hackage.haskell.org/package/base-4.14.0.0/docs/src/Data.Foldable.html#local-6989586621679508611>
(_, y <https://hackage.haskell.org/package/base-4.14.0.0/docs/src/Data.Foldable.html#local-6989586621679508610>)
= f <https://hackage.haskell.org/package/base-4.14.0.0/docs/src/Data.Foldable.html#local-6989586621679508612>
y <https://hackage.haskell.org/package/base-4.14.0.0/docs/src/Data.Foldable.html#local-6989586621679508610>
z <https://hackage.haskell.org/package/base-4.14.0.0/docs/src/Data.Foldable.html#local-6989586621679508611>

We get:
toList (a,b) = [b]

Using the 'natural' property: length = length . toList
We obtain: length (a,b) = length [b] = 1


On Mon, Nov 23, 2020 at 10:22 AM Manuel Schneckenreither <
manuel.schnecki at gmail.com> wrote:

>     >>>>> "HT" == Henning Thielemann <lemming at henning-thielemann.de>
> writes:
>
>     HT> "length (a,b) == 1" is only a consequence of defining instance
>     HT> Foldable for pairs. It was not the argument to implement that
>     HT> instance, at all.
>
> What was the argument to use 1, not 2 for instance?
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From svenpanne at gmail.com  Mon Nov 23 20:18:03 2020
From: svenpanne at gmail.com (Sven Panne)
Date: Mon, 23 Nov 2020 21:18:03 +0100
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at> <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
Message-ID: <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>

Am Mo., 23. Nov. 2020 um 16:32 Uhr schrieb Sebastiaan Joosten <
sjcjoosten+haskell at gmail.com>:

> [...] We obtain: length (a,b) = length [b] = 1
>

Quoting my former self (
https://mail.haskell.org/pipermail/libraries/2017-April/027905.html), you
get even more "fun" stuff with lots of potential for late-night debugging
hours:

   maximum (3,2)   =>   2
   minimum (4,5)   => 5
   sum (6,7)   =>   7
   product (8,9)   =>   9

Yes, you can think of (X, Y) as "Y with context X" or "a one-element
container with Y in it", but is this really what comes to your mind
first? I still highly doubt that. The Foldable-Traversable-in-Prelude
change was largely a good thing, but very surprising (and not really
needed) changes coming stealthily with it were only communicated when
it was already too late... :-/
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From zemyla at gmail.com  Mon Nov 23 20:40:55 2020
From: zemyla at gmail.com (Zemyla)
Date: Mon, 23 Nov 2020 14:40:55 -0600
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at> <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
 <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
Message-ID: <CAK7nUjgGjYbcEOv2pTrVUDQ8U+d8DxeGxM72b-91npgevtQKgw@mail.gmail.com>

So what should maximum (2, "potato") be?

On Mon, Nov 23, 2020, 14:19 Sven Panne <svenpanne at gmail.com> wrote:

> Am Mo., 23. Nov. 2020 um 16:32 Uhr schrieb Sebastiaan Joosten <
> sjcjoosten+haskell at gmail.com>:
>
>> [...] We obtain: length (a,b) = length [b] = 1
>>
>
> Quoting my former self (
> https://mail.haskell.org/pipermail/libraries/2017-April/027905.html), you
> get even more "fun" stuff with lots of potential for late-night debugging
> hours:
>
>    maximum (3,2)   =>   2
>    minimum (4,5)   => 5
>    sum (6,7)   =>   7
>    product (8,9)   =>   9
>
> Yes, you can think of (X, Y) as "Y with context X" or "a one-element container with Y in it", but is this really what comes to your mind first? I still highly doubt that. The Foldable-Traversable-in-Prelude change was largely a good thing, but very surprising (and not really needed) changes coming stealthily with it were only communicated when it was already too late... :-/
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
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From fa-ml at ariis.it  Mon Nov 23 20:45:55 2020
From: fa-ml at ariis.it (Francesco Ariis)
Date: Mon, 23 Nov 2020 21:45:55 +0100
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at>
 <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
 <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
Message-ID: <20201123204555.GA1928@extensa>

Il 23 novembre 2020 alle 21:18 Sven Panne ha scritto:
> Yes, you can think of (X, Y) as "Y with context X" or "a one-element
> container with Y in it", but is this really what comes to your mind
> first? I still highly doubt that. The Foldable-Traversable-in-Prelude
> change was largely a good thing, but very surprising (and not really
> needed) changes coming stealthily with it were only communicated when
> it was already too late... :-/

I recall a long thread, with everyone top posting.
This feature could have helped OP:

    https://gitlab.haskell.org/ghc/ghc/-/issues/11796

but unfortunately is still in design stage
—F

From fa-ml at ariis.it  Mon Nov 23 20:54:26 2020
From: fa-ml at ariis.it (Francesco Ariis)
Date: Mon, 23 Nov 2020 21:54:26 +0100
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <CAK7nUjgGjYbcEOv2pTrVUDQ8U+d8DxeGxM72b-91npgevtQKgw@mail.gmail.com>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at>
 <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
 <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
 <CAK7nUjgGjYbcEOv2pTrVUDQ8U+d8DxeGxM72b-91npgevtQKgw@mail.gmail.com>
Message-ID: <20201123205426.GB1928@extensa>

Il 23 novembre 2020 alle 14:40 Zemyla ha scritto:
> So what should maximum (2, "potato") be?

For people who did not agree with `instance Foldable (,) a`, a
type error!

From tom-lists-haskell-cafe-2017 at jaguarpaw.co.uk  Mon Nov 23 21:22:32 2020
From: tom-lists-haskell-cafe-2017 at jaguarpaw.co.uk (Tom Ellis)
Date: Mon, 23 Nov 2020 21:22:32 +0000
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <20201123205426.GB1928@extensa>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at>
 <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
 <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
 <CAK7nUjgGjYbcEOv2pTrVUDQ8U+d8DxeGxM72b-91npgevtQKgw@mail.gmail.com>
 <20201123205426.GB1928@extensa>
Message-ID: <20201123212232.GU25421@cloudinit-builder>

On Mon, Nov 23, 2020 at 09:54:26PM +0100, Francesco Ariis wrote:
> Il 23 novembre 2020 alle 14:40 Zemyla ha scritto:
> > So what should maximum (2, "potato") be?
> 
> For people who did not agree with `instance Foldable (,) a`, a
> type error!

Which of the following would they give up?

A. Foldable as superclass of Traversable

B. (a,) as Traversable

Personally I think in retrospect I think I'd give up both and use
explicit Traversals (i.e. optics instead).  That way one would have to
write

    allOf each (\ i -> contents p i == contents q i) ...

By contrast

    allOf _2 (\ i -> contents p i == contents q i) ...

obviously looks wrong.

Tom

From lemming at henning-thielemann.de  Mon Nov 23 23:23:17 2020
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Tue, 24 Nov 2020 00:23:17 +0100 (CET)
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <20201123212232.GU25421@cloudinit-builder>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at> <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
 <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
 <CAK7nUjgGjYbcEOv2pTrVUDQ8U+d8DxeGxM72b-91npgevtQKgw@mail.gmail.com>
 <20201123205426.GB1928@extensa>
 <20201123212232.GU25421@cloudinit-builder>
Message-ID: <alpine.DEB.2.20.2011240022290.5933@sputnik>


On Mon, 23 Nov 2020, Tom Ellis wrote:

> On Mon, Nov 23, 2020 at 09:54:26PM +0100, Francesco Ariis wrote:
>> Il 23 novembre 2020 alle 14:40 Zemyla ha scritto:
>> > So what should maximum (2, "potato") be?
>> 
>> For people who did not agree with `instance Foldable (,) a`, a
>> type error!
>
> Which of the following would they give up?
>
> A. Foldable as superclass of Traversable
>
> B. (a,) as Traversable
>
> Personally I think in retrospect I think I'd give up both

You cannot really give up A, because Foldable methods can be implemented 
in terms of traverse.

From amindfv at mailbox.org  Tue Nov 24 07:13:56 2020
From: amindfv at mailbox.org (amindfv at mailbox.org)
Date: Tue, 24 Nov 2020 02:13:56 -0500
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <20201123204555.GA1928@extensa>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at>
 <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
 <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
 <20201123204555.GA1928@extensa>
Message-ID: <20201124071356.GA13199@painter.painter>

On Mon, Nov 23, 2020 at 09:45:55PM +0100, Francesco Ariis wrote:
> Il 23 novembre 2020 alle 21:18 Sven Panne ha scritto:
> > Yes, you can think of (X, Y) as "Y with context X" or "a one-element
> > container with Y in it", but is this really what comes to your mind
> > first? I still highly doubt that. The Foldable-Traversable-in-Prelude
> > change was largely a good thing, but very surprising (and not really
> > needed) changes coming stealthily with it were only communicated when
> > it was already too late... :-/
> 
> I recall a long thread, with everyone top posting.
> This feature could have helped OP:
> 
>     https://gitlab.haskell.org/ghc/ghc/-/issues/11796
> 
> but unfortunately is still in design stage

Fwiw there is at least some strong user interest in this feature if anyone is thinking of working on it. I find myself checking on its progress pretty often, and would use it in our production codebase in a heartbeat.

The strongest motivation is bugs that I've caught during a refactor, where a type somewhere changes from e.g. [x] to (y, [x]), and deep in some function a call to length/maximum/whatever just starts returning useless values without a type error.

Consider, for example:

    do x <- getValuesForId "foo"
       when (length x > 1) $ fail "Unlikely condition: more than one value returned"
       ...

It may be a long time before you discover the 'when' clause will never fire because the type of x has changed to a 2-tuple. In the meantime, you've been doing something wrong with your conflicting data.

Tom

From ietf-dane at dukhovni.org  Tue Nov 24 09:06:22 2020
From: ietf-dane at dukhovni.org (Viktor Dukhovni)
Date: Tue, 24 Nov 2020 04:06:22 -0500
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <20201124071356.GA13199@painter.painter>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at>
 <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
 <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
 <20201123204555.GA1928@extensa>
 <20201124071356.GA13199@painter.painter>
Message-ID: <20201124090622.GE1464@straasha.imrryr.org>

On Tue, Nov 24, 2020 at 02:13:56AM -0500, amindfv--- via Haskell-Cafe wrote:

> Fwiw there is at least some strong user interest in this feature if
> anyone is thinking of working on it. I find myself checking on its
> progress pretty often, and would use it in our production codebase in
> a heartbeat.

Rather than waiting, it is perhaps more pragmatic to go with a custom
Prelude, which one can have now, even for versions of GHC/base, that
won't have the feature in question:

    {-# LANGUAGE NoImplicitPrelude #-}
    module Main (main) where
    import ListPrelude
    import qualified Data.Foldable as F

    main :: IO ()
    main = do
        let { one, two :: Int; one = 1; two = 2 }
        -- OK
        print $ length [one, two]
        print $ F.length (one, two)
        -- Type error
        -- print $ length (one, two)

-- 
    Viktor.
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From jkb at jkbsc.co.uk  Tue Nov 24 09:10:24 2020
From: jkb at jkbsc.co.uk (John Beattie)
Date: Tue, 24 Nov 2020 09:10:24 +0000
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at>
 <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
Message-ID: <20201124091024.GA30993@vatersay>

On 2020-11-23 10:30 -0500, Sebastiaan Joosten wrote:
> length is part of the Foldable class:
> 
> length = foldl' (\c _ -> c+1) 0
> It is probably defined this way s.t. it satisfies:
> length = length . toList
> Not the actual definition, but you can read toList as:
> toList = foldr (:) []
> 
> So as soon as one defines foldr for pairs:
> 
> foldr f z (_, y) = f y z
> 
> We get:
> toList (a,b) = [b]
> 
> Using the 'natural' property: length = length . toList
> We obtain: length (a,b) = length [b] = 1
> 
> 
> On Mon, Nov 23, 2020 at 10:22 AM Manuel Schneckenreither <
> manuel.schnecki at gmail.com> wrote:
> 
>         >>>>> "HT" == Henning Thielemann <lemming at henning-thielemann.de>
>     writes:
> 
>         HT> "length (a,b) == 1" is only a consequence of defining instance
>         HT> Foldable for pairs. It was not the argument to implement that
>         HT> instance, at all.
> 
>     What was the argument to use 1, not 2 for instance?

ok, but why define foldr like that?

A long time ago, I saw an exposition of lists in an imperative setting which
treated them as pairs of (value, pointer) where the pointer pointed to the next
item. If we start with the above folder for pairs, I think we wouldn't get the
usual foldr on lists defined in this way from pairs, no?

Ok, I see, pairs are used for lots of things, including lists. They could also
be used as the basis for longer tuples.

Another suggestion, why don't we define foldr via currying:

foldr f z (x,y) = f z x y   ?

From lemming at henning-thielemann.de  Tue Nov 24 09:20:58 2020
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Tue, 24 Nov 2020 10:20:58 +0100 (CET)
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <20201124090622.GE1464@straasha.imrryr.org>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
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 <20201124090622.GE1464@straasha.imrryr.org>
Message-ID: <alpine.DEB.2.20.2011241012430.5555@sputnik>


On Tue, 24 Nov 2020, Viktor Dukhovni wrote:

> Rather than waiting, it is perhaps more pragmatic to go with a custom
> Prelude, which one can have now, even for versions of GHC/base, that
> won't have the feature in question:

I have such a Prelude:
    https://hackage.haskell.org/package/prelude-compat

It helps a bit, but does not fully solve the problem.

If you use Fold.all on a Map and then switch from Map k a to (Map k a, b) 
you will again not encounter a warning nor a type error.



I had the idea of implementing forbidden instances like:

instance Unsatisfiable a => Foldable ((,) a) where

If I use them (or import them?) they would conflict with the one from 
FTP-Prelude. I have not tried that idea. It might exclude importing code 
that uses Foldable on pair intentionally.

From manuel.schnecki at gmail.com  Tue Nov 24 09:55:21 2020
From: manuel.schnecki at gmail.com (Manuel Schneckenreither)
Date: Tue, 24 Nov 2020 10:55:21 +0100
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <20201123212232.GU25421@cloudinit-builder>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at> <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
 <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
 <CAK7nUjgGjYbcEOv2pTrVUDQ8U+d8DxeGxM72b-91npgevtQKgw@mail.gmail.com>
 <20201123205426.GB1928@extensa> <20201123212232.GU25421@cloudinit-builder>
Message-ID: <CABA4qkcOPet=aR-hwgoXeK8eVmGeYr5RLM2LWGCRiiTPND0+oQ@mail.gmail.com>

    >>>>> "TE" == Tom Ellis <tom-lists-haskell-cafe-2017 at jaguarpaw.co.uk>
writes:

    TE> On Mon, Nov 23, 2020 at 09:54:26PM +0100, Francesco Ariis wrote:

    TE> Which of the following would they give up?

    TE> A. Foldable as superclass of Traversable

    TE> B. (a,) as Traversable

For me it is B. Even the Foldable hackage description states "Functors
representing data structures that can be traversed from left to right."
The tuple is however not traversed from left to right, but solely on the
right (as it's half filled).

For me it doesn't make sense to implement it, just because it's
implementable. I think the current implementation does not add more
value than it harms.


El lun., 23 nov. 2020 22:23, Tom Ellis <
tom-lists-haskell-cafe-2017 at jaguarpaw.co.uk> escribió:

> On Mon, Nov 23, 2020 at 09:54:26PM +0100, Francesco Ariis wrote:
> > Il 23 novembre 2020 alle 14:40 Zemyla ha scritto:
> > > So what should maximum (2, "potato") be?
> >
> > For people who did not agree with `instance Foldable (,) a`, a
> > type error!
>
> Which of the following would they give up?
>
> A. Foldable as superclass of Traversable
>
> B. (a,) as Traversable
>
> Personally I think in retrospect I think I'd give up both and use
> explicit Traversals (i.e. optics instead).  That way one would have to
> write
>
>     allOf each (\ i -> contents p i == contents q i) ...
>
> By contrast
>
>     allOf _2 (\ i -> contents p i == contents q i) ...
>
> obviously looks wrong.
>
> Tom
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From b at chreekat.net  Tue Nov 24 13:20:16 2020
From: b at chreekat.net (Bryan Richter)
Date: Tue, 24 Nov 2020 15:20:16 +0200
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <CABA4qkcOPet=aR-hwgoXeK8eVmGeYr5RLM2LWGCRiiTPND0+oQ@mail.gmail.com>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at> <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
 <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
 <CAK7nUjgGjYbcEOv2pTrVUDQ8U+d8DxeGxM72b-91npgevtQKgw@mail.gmail.com>
 <20201123205426.GB1928@extensa> <20201123212232.GU25421@cloudinit-builder>
 <CABA4qkcOPet=aR-hwgoXeK8eVmGeYr5RLM2LWGCRiiTPND0+oQ@mail.gmail.com>
Message-ID: <CAH9BU=z3cvZ7_yZzNL-rKFDFj6X=EfWo=KOStvjxneM0qud7Hg@mail.gmail.com>

In homage to the ironic phrase "It's technically true, which is the best
kind of true," perhaps we need a superclass TechnicallyFoldable. :D Then
(,) a could be an instance of TechnicallyFoldable but not Foldable ,
tlength could be defined as tlength = length for (Foldable a =>
TechnicallyFoldable a), and anybody who really wants the maximally general
option could always use tlength.

The parallel with fmap speaks for itself. :)

Den tis 24 nov. 2020 11:56Manuel Schneckenreither <manuel.schnecki at gmail.com>
skrev:

>     >>>>> "TE" == Tom Ellis <tom-lists-haskell-cafe-2017 at jaguarpaw.co.uk>
> writes:
>
>     TE> On Mon, Nov 23, 2020 at 09:54:26PM +0100, Francesco Ariis wrote:
>
>     TE> Which of the following would they give up?
>
>     TE> A. Foldable as superclass of Traversable
>
>     TE> B. (a,) as Traversable
>
> For me it is B. Even the Foldable hackage description states "Functors
> representing data structures that can be traversed from left to right."
> The tuple is however not traversed from left to right, but solely on the
> right (as it's half filled).
>
> For me it doesn't make sense to implement it, just because it's
> implementable. I think the current implementation does not add more
> value than it harms.
>
>
> El lun., 23 nov. 2020 22:23, Tom Ellis <
> tom-lists-haskell-cafe-2017 at jaguarpaw.co.uk> escribió:
>
>> On Mon, Nov 23, 2020 at 09:54:26PM +0100, Francesco Ariis wrote:
>> > Il 23 novembre 2020 alle 14:40 Zemyla ha scritto:
>> > > So what should maximum (2, "potato") be?
>> >
>> > For people who did not agree with `instance Foldable (,) a`, a
>> > type error!
>>
>> Which of the following would they give up?
>>
>> A. Foldable as superclass of Traversable
>>
>> B. (a,) as Traversable
>>
>> Personally I think in retrospect I think I'd give up both and use
>> explicit Traversals (i.e. optics instead).  That way one would have to
>> write
>>
>>     allOf each (\ i -> contents p i == contents q i) ...
>>
>> By contrast
>>
>>     allOf _2 (\ i -> contents p i == contents q i) ...
>>
>> obviously looks wrong.
>>
>> Tom
>> _______________________________________________
>> Haskell-Cafe mailing list
>> To (un)subscribe, modify options or view archives go to:
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>> Only members subscribed via the mailman list are allowed to post.
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From ietf-dane at dukhovni.org  Tue Nov 24 18:49:14 2020
From: ietf-dane at dukhovni.org (Viktor Dukhovni)
Date: Tue, 24 Nov 2020 13:49:14 -0500
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <alpine.DEB.2.20.2011241012430.5555@sputnik>
References: <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at>
 <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
 <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
 <20201123204555.GA1928@extensa>
 <20201124071356.GA13199@painter.painter>
 <20201124090622.GE1464@straasha.imrryr.org>
 <alpine.DEB.2.20.2011241012430.5555@sputnik>
Message-ID: <20201124184914.GF1464@straasha.imrryr.org>

On Tue, Nov 24, 2020 at 10:20:58AM +0100, Henning Thielemann wrote:

> > Rather than waiting, it is perhaps more pragmatic to go with a custom
> > Prelude, which one can have now, even for versions of GHC/base, that
> > won't have the feature in question:
> 
> I have such a Prelude:
>     https://hackage.haskell.org/package/prelude-compat
> 
> It helps a bit, but does not fully solve the problem.
> 
> If you use Fold.all on a Map and then switch from Map k a to (Map k a, b) 
> you will again not encounter a warning nor a type error.

Yes, for that one might have to be disciplined and use a monomorphised
variant:

    allMapValues :: (a -> Bool) -> Map k a -> Bool
    allMapValues = Data.Foldable.all

although the risk is only present when (a ~ b), or the predicate is
sufficiently polymorphic (over some superclass of `a` and `b`).

And of course, when refactoring, instead of moving to a 2-tuple, that
brings in possibly unwanted instances, one can instead choose a custom
product type, that does not have a Foldable instance:

    -- coercible to a 2-tuple if/as needed
    newtype T2 a b = T2 { _unT2 :: (a, b) } deriving (Eq, Ord, Show)

to give one's 2-tuples exactly the desired instances and no more.  This
admittedly is not terribly ergonomic.

-- 
    Viktor.

From lemming at henning-thielemann.de  Tue Nov 24 19:40:34 2020
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Tue, 24 Nov 2020 20:40:34 +0100 (CET)
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <20201124184914.GF1464@straasha.imrryr.org>
References: <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at> <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
 <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
 <20201123204555.GA1928@extensa> <20201124071356.GA13199@painter.painter>
 <20201124090622.GE1464@straasha.imrryr.org>
 <alpine.DEB.2.20.2011241012430.5555@sputnik>
 <20201124184914.GF1464@straasha.imrryr.org>
Message-ID: <alpine.DEB.2.20.2011242038540.5555@sputnik>


On Tue, 24 Nov 2020, Viktor Dukhovni wrote:

> And of course, when refactoring, instead of moving to a 2-tuple, that 
> brings in possibly unwanted instances, one can instead choose a custom 
> product type, that does not have a Foldable instance:
>
>    -- coercible to a 2-tuple if/as needed
>    newtype T2 a b = T2 { _unT2 :: (a, b) } deriving (Eq, Ord, Show)
>
> to give one's 2-tuples exactly the desired instances and no more.  This 
> admittedly is not terribly ergonomic.

If people would use custom pair types we would not need Foldable on pairs, 
at all.

From twilson at csufresno.edu  Tue Nov 24 22:26:03 2020
From: twilson at csufresno.edu (Todd Wilson)
Date: Tue, 24 Nov 2020 14:26:03 -0800
Subject: [Haskell-cafe] Types of partially instantiated polymorphic helper
	functions
Message-ID: <CA+-99oLq1SC2_aoQSYw101vH07CUtiLwbEM8H5eXqdak=0gN-w@mail.gmail.com>

Dear Cafe,

This has got to be a trivial question, but I don't see a solution, nor
could I find anything through searching: If I want to write a type
declaration for the helper function g here, what do I write?

f :: a -> [b] -> [(a,b)]
f a bs = g bs where
  g :: ????
  g [] = []
  g (x:xs) = (a,x) : g xs


Apologies if I'm wasting bandwidth with my ignorance.

Todd Wilson
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From adam at well-typed.com  Tue Nov 24 22:37:38 2020
From: adam at well-typed.com (Adam Gundry)
Date: Tue, 24 Nov 2020 22:37:38 +0000
Subject: [Haskell-cafe] Types of partially instantiated polymorphic
 helper functions
In-Reply-To: <CA+-99oLq1SC2_aoQSYw101vH07CUtiLwbEM8H5eXqdak=0gN-w@mail.gmail.com>
References: <CA+-99oLq1SC2_aoQSYw101vH07CUtiLwbEM8H5eXqdak=0gN-w@mail.gmail.com>
Message-ID: <af507a6d-aadc-d668-adb2-d31726163a87@well-typed.com>

Dear Todd,

On 24/11/2020 22:26, Todd Wilson wrote:
> This has got to be a trivial question, but I don't see a solution, nor
> could I find anything through searching: If I want to write a type
> declaration for the helper function g here, what do I write?
> 
>     f :: a -> [b] -> [(a,b)]
>     f a bs = g bs where
>       g :: ????
>       g [] = []
>       g (x:xs) = (a,x) : g xs

This has a disappointingly not-entirely-trivial answer:

    {-# LANGUAGE ExplicitForAll, ScopedTypeVariables #-}

    f :: forall a b . a -> [b] -> [(a,b)]
    f a bs = g bs where
      g :: [c] -> [(a, c)]
      g [] = []
      g (x:xs) = (a,x) : g xs

We need the type variable `a` in the type of `g` to be the same as the
one bound in the type of `f`, but Haskell2010 doesn't have a way to
express this. The ScopedTypeVariables extension, when used with an
explicit forall, makes the type variables scope over type signatures in
the body of the function.

Hope this helps,

Adam

-- 
Adam Gundry, Haskell Consultant
Well-Typed LLP, https://www.well-typed.com/

Registered in England & Wales, OC335890
118 Wymering Mansions, Wymering Road, London W9 2NF, England

From tom-lists-haskell-cafe-2017 at jaguarpaw.co.uk  Tue Nov 24 22:37:40 2020
From: tom-lists-haskell-cafe-2017 at jaguarpaw.co.uk (Tom Ellis)
Date: Tue, 24 Nov 2020 22:37:40 +0000
Subject: [Haskell-cafe] Types of partially instantiated polymorphic
 helper functions
In-Reply-To: <CA+-99oLq1SC2_aoQSYw101vH07CUtiLwbEM8H5eXqdak=0gN-w@mail.gmail.com>
References: <CA+-99oLq1SC2_aoQSYw101vH07CUtiLwbEM8H5eXqdak=0gN-w@mail.gmail.com>
Message-ID: <20201124223740.GB22702@cloudinit-builder>

On Tue, Nov 24, 2020 at 02:26:03PM -0800, Todd Wilson wrote:
> This has got to be a trivial question, but I don't see a solution, nor
> could I find anything through searching: If I want to write a type
> declaration for the helper function g here, what do I write?
> 
> f :: a -> [b] -> [(a,b)]
> f a bs = g bs where
>   g :: ????
>   g [] = []
>   g (x:xs) = (a,x) : g xs

You probably want this:


{-# LANGUAGE ScopedTypeVariables #-}

f :: forall a b. a -> [b] -> [(a,b)]
f a bs = g bs where
  g :: [b'] -> [(a, b')]
  g [] = []
  g (x:xs) = (a,x) : g xs

From olf at aatal-apotheke.de  Tue Nov 24 22:52:12 2020
From: olf at aatal-apotheke.de (Olaf Klinke)
Date: Tue, 24 Nov 2020 23:52:12 +0100
Subject: [Haskell-cafe] What to call Occult Effects
Message-ID: <68b5d585528f504859b0765c8922fa162bae2963.camel@aatal-apotheke.de>

> Dear Olaf and everyone,
> 
> the law do {_ <- b; a} = a is equivalent to do {_ <- b; return ()} =
> return (), for, assuming the latter,
> 
>           do {_ <- b; a}
>         = do {_ <- do {_ <- b; return ()}; a}
>         = do {_ <- return (); a}
>         = a
> 
> and it does actually have some history. It was dubbed
> 'discardability' by Thielecke [1] and explored by 
> Führmann in [2] together with some other important properties of
> effects, such as 'centrality' and 
> 'commutativity'. Combinations of these properties and examples are
> explored in the conventional 
> Haskell-like style in [3] (where 'discardability' is called 'side-
> effect freeness' though).
> 
> Cheers,
> Sergey
> 
> [1] H. Thielecke, Categorical structure of continuation passing
> style, Ph.D. Thesis, University of 
> Edinburgh, 1997.
> 
> [2] C. Führmann, Varieties of effects, in: M. Nielsen, U. Engberg
> (Eds.), Foundations of Software 
> Science and Computation Structures, FOSSACS 2002, in: Lect. Notes
> Comput. Sci., vol. 2303, Springer,
> 2002, pp. 144–158.
> 
> [3] L. Schröder, T. Mossakowski, Monad-independent dynamic logic in
> HasCasl, J. Logic Comput. 14 (2004) 
> 571–619

I've got the impression that all three of the above works look at a
problem dual to the OP in a certain sense: At least [1] and [2] ask:
For a given monad M, what is the subset of computations b with 
b >> a = a for all a?
In contrast, I understood Kim-Ee's question as: What are the monads M
where all computations b belong to this class? 

Assuming this property, the monoid M () is isomorphic to (). 
Indeed, the monoid M () inherits the property 
a <> b = b
for all a, b :: M () and the only monoid with this property is the one-
element monoid. 

In category theory a monad M with M 1 being isomorphic to the terminal
object 1 is called 'affine'. Bart Jacobs in [4] gives a diagram (10)
that amounts to 
return.const = fmap.const
and shows that this is equivalent to being affine. Hence we might also
use 'affine' for monads with Kim-Ee's property. Bart Jacobs' proof
first reduces the  general identity 

return.const = fmap.const :: a -> m b -> m a

to the case b = () just as Sergey did above. Then
= fmap (const a)
= fmap (const a) . (id :: m () -> m ())
= fmap (const a) . return . const ()     by assumption
= return . const a . const ()            by naturality of return
= return . const a                       property of const

I also learned that the school of 'effects' tries to avoid monads (this
going back to John Power), so the terms 'discardable' and 'affine'
might just be names for the same thing in different communities. 

Further there is a categorical construction (see [4]) to compute the
greatest affine sub-monad of a monad. Interestingly, the affine part of
the state monad is the reader monad, that is, functions 
s -> (a,s) 
that may use s but not change it. 


Olaf


[4] https://hal.inria.fr/hal-01446033/file/418352_1_En_5_Chapter.pdf


From twilson at csufresno.edu  Tue Nov 24 22:58:33 2020
From: twilson at csufresno.edu (Todd Wilson)
Date: Tue, 24 Nov 2020 14:58:33 -0800
Subject: [Haskell-cafe] Types of partially instantiated polymorphic
	helper functions
In-Reply-To: <af507a6d-aadc-d668-adb2-d31726163a87@well-typed.com>
References: <CA+-99oLq1SC2_aoQSYw101vH07CUtiLwbEM8H5eXqdak=0gN-w@mail.gmail.com>
 <af507a6d-aadc-d668-adb2-d31726163a87@well-typed.com>
Message-ID: <CA+-99oKcKa29=LTGF4DRYb4V-xpcfGabcn9HgubxctvVqwtbEw@mail.gmail.com>

I see, thanks! And I guess that if the type variable c in your type of g
were changed to b, it will still work, but now g would have a monomorphic
instead of polymorphic type. I hope the combination of keywords in my
subject line can serve to direct someone else with this problem to your
answer!

Todd Wilson

On Tue, Nov 24, 2020 at 2:37 PM Adam Gundry <adam at well-typed.com> wrote:

> Dear Todd,
>
> On 24/11/2020 22:26, Todd Wilson wrote:
> > This has got to be a trivial question, but I don't see a solution, nor
> > could I find anything through searching: If I want to write a type
> > declaration for the helper function g here, what do I write?
> >
> >     f :: a -> [b] -> [(a,b)]
> >     f a bs = g bs where
> >       g :: ????
> >       g [] = []
> >       g (x:xs) = (a,x) : g xs
>
> This has a disappointingly not-entirely-trivial answer:
>
>     {-# LANGUAGE ExplicitForAll, ScopedTypeVariables #-}
>
>     f :: forall a b . a -> [b] -> [(a,b)]
>     f a bs = g bs where
>       g :: [c] -> [(a, c)]
>       g [] = []
>       g (x:xs) = (a,x) : g xs
>
> We need the type variable `a` in the type of `g` to be the same as the
> one bound in the type of `f`, but Haskell2010 doesn't have a way to
> express this. The ScopedTypeVariables extension, when used with an
> explicit forall, makes the type variables scope over type signatures in
> the body of the function.
>
> Hope this helps,
>
> Adam
>
> --
> Adam Gundry, Haskell Consultant
> Well-Typed LLP, https://www.well-typed.com/
>
> Registered in England & Wales, OC335890
> 118 Wymering Mansions, Wymering Road, London W9 2NF, England
>
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From ietf-dane at dukhovni.org  Tue Nov 24 23:38:30 2020
From: ietf-dane at dukhovni.org (Viktor Dukhovni)
Date: Tue, 24 Nov 2020 18:38:30 -0500
Subject: [Haskell-cafe] Types of partially instantiated polymorphic
 helper functions
In-Reply-To: <CA+-99oKcKa29=LTGF4DRYb4V-xpcfGabcn9HgubxctvVqwtbEw@mail.gmail.com>
References: <CA+-99oLq1SC2_aoQSYw101vH07CUtiLwbEM8H5eXqdak=0gN-w@mail.gmail.com>
 <af507a6d-aadc-d668-adb2-d31726163a87@well-typed.com>
 <CA+-99oKcKa29=LTGF4DRYb4V-xpcfGabcn9HgubxctvVqwtbEw@mail.gmail.com>
Message-ID: <20201124233830.GI1464@straasha.imrryr.org>

On Tue, Nov 24, 2020 at 02:58:33PM -0800, Todd Wilson wrote:

> I see, thanks! And I guess that if the type variable c in your type of g
> were changed to b, it will still work, but now g would have a monomorphic
> instead of polymorphic type.

Yes, exactly.  I was not going to post my otherwise redundant
answer, but since it in fact makes `g` monomorphic, here it is:

The simplest thing (which you probably already know) is to not give `g`                                                                                                                      a type signature, and let GHC infer the type.  But since you asked,                                                                                                                          one solution is:

    {-# LANGUAGE ScopedTypeVariables #-}

    f :: forall a b. a -> [b] -> [(a, b)]
    f a bs = g bs where
      g :: [b] -> [(a, b)]
      g [] = []
      g (x:xs) = (a, x) : g xs

You need scoped type variables becase the `a` in the return-type of `g`
needs to be the *same* `a` as in the signature of `f`, and unlike `f`
the function `g` is not polymorphic in `a`, so you need a mechanis to
identify the two instances of the type variable, and that's where the
`ScopedTypeVariables` pragma comes into play.

Once you have `ScopedTypeVariables`, you also get (for free)
`ExplicitForall`, and each new universally quanitified type
variable now needs "forall" to bring it into scope.

-- 
    Viktor.

From sergey.goncharov at fau.de  Tue Nov 24 23:48:02 2020
From: sergey.goncharov at fau.de (Sergey Goncharov)
Date: Wed, 25 Nov 2020 00:48:02 +0100
Subject: [Haskell-cafe] What to call Occult Effects
In-Reply-To: <68b5d585528f504859b0765c8922fa162bae2963.camel@aatal-apotheke.de>
References: <68b5d585528f504859b0765c8922fa162bae2963.camel@aatal-apotheke.de>
Message-ID: <6c56d096-b199-9ff7-bb0f-99c85ef787e8@fau.de>

Dear Olaf,

>>
>> [1] H. Thielecke, Categorical structure of continuation passing
>> style, Ph.D. Thesis, University of
>> Edinburgh, 1997.
>>
>> [2] C. Führmann, Varieties of effects, in: M. Nielsen, U. Engberg
>> (Eds.), Foundations of Software
>> Science and Computation Structures, FOSSACS 2002, in: Lect. Notes
>> Comput. Sci., vol. 2303, Springer,
>> 2002, pp. 144–158.
>>
>> [3] L. Schröder, T. Mossakowski, Monad-independent dynamic logic in
>> HasCasl, J. Logic Comput. 14 (2004)
>> 571–619
> 
> I've got the impression that all three of the above works look at a
> problem dual to the OP in a certain sense: At least [1] and [2] ask:
> For a given monad M, what is the subset of computations b with
> b >> a = a for all a?
> In contrast, I understood Kim-Ee's question as: What are the monads M
> where all computations b belong to this class?

Well, these two questions are closely related, as you actually indicate further below. In [1] the main 
monad is the continuation monad, and equational laws are used as means to classify classes of 
computations with important properties, but nothing prevents one from using them for classifying monads 
entirely satisfying such laws.

> 
> Assuming this property, the monoid M () is isomorphic to ().
> Indeed, the monoid M () inherits the property
> a <> b = b
> for all a, b :: M () and the only monoid with this property is the one-
> element monoid.
> 
> In category theory a monad M with M 1 being isomorphic to the terminal
> object 1 is called 'affine'. Bart Jacobs in [4] gives a diagram (10)
> that amounts to
> return.const = fmap.const
> and shows that this is equivalent to being affine. Hence we might also
> use 'affine' for monads with Kim-Ee's property. Bart Jacobs' proof
> first reduces the  general identity
> 
> return.const = fmap.const :: a -> m b -> m a
> 
> to the case b = () just as Sergey did above. Then
> = fmap (const a)
> = fmap (const a) . (id :: m () -> m ())
> = fmap (const a) . return . const ()     by assumption
> = return . const a . const ()            by naturality of return
> = return . const a                       property of const
> 

Yes, it is again just the same law: isomorphism of M () and () is a yet more concise way to state this 
property, neat!

> I also learned that the school of 'effects' tries to avoid monads (this
> going back to John Power), so the terms 'discardable' and 'affine'
> might just be names for the same thing in different communities.
> 
> Further there is a categorical construction (see [4]) to compute the
> greatest affine sub-monad of a monad. Interestingly, the affine part of
> the state monad is the reader monad, that is, functions
> s -> (a,s)
> that may use s but not change it.
> 

I think [3] and [4] are related (and somewhat contrast [1] and [2]) in that, the laws like 
discardability are meant to identify those computations (or (sub-)monad), which can in a way play a role 
of logical assertions. So, the slogan is: assertions are well-behaved computations.

In that sense, from the perspective of [3], discardability is a desirable property, but not sufficient. 
For example, the 'copyability law'

	do {x <- p; y <- p; return (x, y)} = do {x <- p; return (x, x)}

is not satisfied by the probability distribution monad, which is discardable, roughly, because when 
tossing a coin, getting tails twice in a row is 1/4, while the probability of getting tails after 
tossing it once is 1/2. So, if we regard sequential composition of programs as a kind of conjunction, 
then it would not be idempotent.

 From the perspective of [4], not having copyability is fine, because the underlying logic is meant to 
be more permissive, and admits non-idempotent conjunctions. Same goes for commutativity: even the 
conjunction of copyability and discardability does not entail commutativity -- [3] contains a 
counterexample to this effect (Example 37).

Cheers,
Sergey

> 
> Olaf
> 
> 
> [4] https://hal.inria.fr/hal-01446033/file/418352_1_En_5_Chapter.pdf
> 

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From lemming at henning-thielemann.de  Tue Nov 24 23:50:58 2020
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Wed, 25 Nov 2020 00:50:58 +0100 (CET)
Subject: [Haskell-cafe] Types of partially instantiated polymorphic
 helper functions
In-Reply-To: <20201124233830.GI1464@straasha.imrryr.org>
References: <CA+-99oLq1SC2_aoQSYw101vH07CUtiLwbEM8H5eXqdak=0gN-w@mail.gmail.com>
 <af507a6d-aadc-d668-adb2-d31726163a87@well-typed.com>
 <CA+-99oKcKa29=LTGF4DRYb4V-xpcfGabcn9HgubxctvVqwtbEw@mail.gmail.com>
 <20201124233830.GI1464@straasha.imrryr.org>
Message-ID: <alpine.DEB.2.20.2011250049210.5555@sputnik>


On Tue, 24 Nov 2020, Viktor Dukhovni wrote:

> On Tue, Nov 24, 2020 at 02:58:33PM -0800, Todd Wilson wrote:
>
>> I see, thanks! And I guess that if the type variable c in your type of g
>> were changed to b, it will still work, but now g would have a monomorphic
>> instead of polymorphic type.
>
> Yes, exactly.  I was not going to post my otherwise redundant
> answer, but since it in fact makes `g` monomorphic, here it is:
>
> The simplest thing (which you probably already know) is to not give `g`                                                                                                                      a type signature, and let GHC infer the type.  But since you asked,                                                                                                                          one solution is:
>
>    {-# LANGUAGE ScopedTypeVariables #-}
>
>    f :: forall a b. a -> [b] -> [(a, b)]
>    f a bs = g bs where
>      g :: [b] -> [(a, b)]
>      g [] = []
>      g (x:xs) = (a, x) : g xs

An alternative would be to let g be polymorphic but add 'a' as parameter:

   f a bs = g a bs where
      g :: a -> [b] -> [(a, b)]
      g = map ((,) a)

From stuart.hungerford at gmail.com  Wed Nov 25 03:29:16 2020
From: stuart.hungerford at gmail.com (Stuart Hungerford)
Date: Wed, 25 Nov 2020 14:29:16 +1100
Subject: [Haskell-cafe] Looking for idiomatic example of wrapping a Haskell
	library
Message-ID: <CAG+kMrEvpYis6-obTgO5KfKNwRz=Yt3yCAy_RpmeeYLhuRMmvA@mail.gmail.com>

Hi Haskellers,

In a Haskell learning project I'm looking at using a couple of Haskell
packages (from Hackage) for linear algebra and graphics.

I've got a strong feeling my choices of these libraries are going to
change as the project progresses and to avoid having to change
references to these library functions throughout my modules I'd like
to "wrap" them in modules of my own. Can anyone point me to a project
where a Haskell library has been idiomatically wrapped this way?

I can see newtypes and "smart" constructors of the wrapped types will
go some way towards this, but I suspect there's more techniques I
haven't yet learned.

Thanks in advance,

Stu

From david.feuer at gmail.com  Wed Nov 25 03:38:19 2020
From: david.feuer at gmail.com (David Feuer)
Date: Tue, 24 Nov 2020 22:38:19 -0500
Subject: [Haskell-cafe] Looking for idiomatic example of wrapping a
 Haskell library
In-Reply-To: <CAG+kMrEvpYis6-obTgO5KfKNwRz=Yt3yCAy_RpmeeYLhuRMmvA@mail.gmail.com>
References: <CAG+kMrEvpYis6-obTgO5KfKNwRz=Yt3yCAy_RpmeeYLhuRMmvA@mail.gmail.com>
Message-ID: <CAMgWh9u9Vih0rJMLcZc-UmX_8Jq=dT37jX2h3yBvAKzKN3-U5A@mail.gmail.com>

For the specific choices of linear algebra and graphics, I'm going to go
out on a limb and guess you probably don't want to do that. Different
frameworks have radically different APIs, so a "generic" wrapper is likely
to give you a slow subset of the functionality of each package.

On Tue, Nov 24, 2020, 10:29 PM Stuart Hungerford <
stuart.hungerford at gmail.com> wrote:

> Hi Haskellers,
>
> In a Haskell learning project I'm looking at using a couple of Haskell
> packages (from Hackage) for linear algebra and graphics.
>
> I've got a strong feeling my choices of these libraries are going to
> change as the project progresses and to avoid having to change
> references to these library functions throughout my modules I'd like
> to "wrap" them in modules of my own. Can anyone point me to a project
> where a Haskell library has been idiomatically wrapped this way?
>
> I can see newtypes and "smart" constructors of the wrapped types will
> go some way towards this, but I suspect there's more techniques I
> haven't yet learned.
>
> Thanks in advance,
>
> Stu
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
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From stuart.hungerford at gmail.com  Wed Nov 25 04:08:28 2020
From: stuart.hungerford at gmail.com (Stuart Hungerford)
Date: Wed, 25 Nov 2020 15:08:28 +1100
Subject: [Haskell-cafe] Looking for idiomatic example of wrapping a
 Haskell library
In-Reply-To: <CAMgWh9u9Vih0rJMLcZc-UmX_8Jq=dT37jX2h3yBvAKzKN3-U5A@mail.gmail.com>
References: <CAG+kMrEvpYis6-obTgO5KfKNwRz=Yt3yCAy_RpmeeYLhuRMmvA@mail.gmail.com>
 <CAMgWh9u9Vih0rJMLcZc-UmX_8Jq=dT37jX2h3yBvAKzKN3-U5A@mail.gmail.com>
Message-ID: <CAG+kMrEw3K9OSouVMChX9Y-LvPCBkvTCOTWgXGKqHpFLK02ghQ@mail.gmail.com>

On Wed, Nov 25, 2020 at 2:38 PM David Feuer <david.feuer at gmail.com> wrote:

> For the specific choices of linear algebra and graphics, I'm going to go out on a limb and guess you probably don't want to do that. Different frameworks have radically different APIs, so a "generic" wrapper is likely to give you a slow subset of the functionality of each package.

Thanks David -- that's a good point I hadn't really considered.

Stu

From barak at pearlmutter.net  Wed Nov 25 14:05:43 2020
From: barak at pearlmutter.net (Barak A. Pearlmutter)
Date: Wed, 25 Nov 2020 14:05:43 +0000
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,)a)
In-Reply-To: <mailman.1.1606305601.4495.haskell-cafe@haskell.org>
References: <mailman.1.1606305601.4495.haskell-cafe@haskell.org>
Message-ID: <CANa01B+R6r2zQ+EKD-RkntZVhxfioFBgStV47=FcPx4udOprCw@mail.gmail.com>

On Tue, 24 Nov 2020, Henning Thielemann wrote:

> If people would use custom pair types we would not need Foldable on pairs,
> at all.

To be fair, if people would use custom pair types we would not need
*pairs* at all.

--Barak Pearlmutter

From zemyla at gmail.com  Wed Nov 25 17:26:04 2020
From: zemyla at gmail.com (Zemyla)
Date: Wed, 25 Nov 2020 11:26:04 -0600
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,)a)
In-Reply-To: <CANa01B+R6r2zQ+EKD-RkntZVhxfioFBgStV47=FcPx4udOprCw@mail.gmail.com>
References: <mailman.1.1606305601.4495.haskell-cafe@haskell.org>
 <CANa01B+R6r2zQ+EKD-RkntZVhxfioFBgStV47=FcPx4udOprCw@mail.gmail.com>
Message-ID: <CAK7nUjgBbmOU0rgL7uF_+3Qx+1JxoKSBOyQq3s3uFch8zGLvJg@mail.gmail.com>

Except we would, because we need to be able to express instances like first
in Arrow using builtin pairs, rather than try and write some sort of
combination for every pair and arrow. And I'm pretty sure there are other
libraries which depend on pairs too.

On Wed, Nov 25, 2020, 08:07 Barak A. Pearlmutter <barak at pearlmutter.net>
wrote:

> On Tue, 24 Nov 2020, Henning Thielemann wrote:
>
> > If people would use custom pair types we would not need Foldable on
> pairs,
> > at all.
>
> To be fair, if people would use custom pair types we would not need
> *pairs* at all.
>
> --Barak Pearlmutter
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From ietf-dane at dukhovni.org  Wed Nov 25 17:52:56 2020
From: ietf-dane at dukhovni.org (Viktor Dukhovni)
Date: Wed, 25 Nov 2020 15:52:56 -0200
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,)a)
In-Reply-To: <CAK7nUjgBbmOU0rgL7uF_+3Qx+1JxoKSBOyQq3s3uFch8zGLvJg@mail.gmail.com>
References: <mailman.1.1606305601.4495.haskell-cafe@haskell.org>
 <CANa01B+R6r2zQ+EKD-RkntZVhxfioFBgStV47=FcPx4udOprCw@mail.gmail.com>
 <CAK7nUjgBbmOU0rgL7uF_+3Qx+1JxoKSBOyQq3s3uFch8zGLvJg@mail.gmail.com>
Message-ID: <51B7EC49-CDA2-4CFF-93D8-25830CADC824@dukhovni.org>

> On Nov 25, 2020, at 3:26 PM, Zemyla <zemyla at gmail.com> wrote:
> 
> Except we would, because we need to be able to express instances like first in Arrow using builtin pairs, rather than try and write some sort of combination for every pair and arrow. And I'm pretty sure there are other libraries which depend on pairs too.

This is why I posted the not terribly ergonomic:

	newtype T2 a b = T2 { _unT2 :: (a, b) }

which has a free coercion to a pair, so you can pass a pair
to any library that needs one, without any runtime overhead.

This of course takes much discipline to use when refactoring
data types, in order to avoid missing needed changes obscured
by unwanted instances of the built-in pair.

Wherever you need a pair, you'd have to write "(coerce t2)",
rather than "t2".

-- 
	Viktor.


From barak at pearlmutter.net  Wed Nov 25 19:56:49 2020
From: barak at pearlmutter.net (Barak A. Pearlmutter)
Date: Wed, 25 Nov 2020 19:56:49 +0000
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,)a)
In-Reply-To: <CAK7nUjgBbmOU0rgL7uF_+3Qx+1JxoKSBOyQq3s3uFch8zGLvJg@mail.gmail.com>
References: <mailman.1.1606305601.4495.haskell-cafe@haskell.org>
 <CANa01B+R6r2zQ+EKD-RkntZVhxfioFBgStV47=FcPx4udOprCw@mail.gmail.com>
 <CAK7nUjgBbmOU0rgL7uF_+3Qx+1JxoKSBOyQq3s3uFch8zGLvJg@mail.gmail.com>
Message-ID: <CANa01BK_KnQ7f2UnqYDgqWkmQ5_K3cMwbDbCzRX94zT9qfv5+w@mail.gmail.com>

True. And their use in Arrow is a great example of pairs that do *not*
work well as instances of Foldable as currently defined. Arrow is
using pairs as abstract Cartesian products, and the natural
isomorphism A×B≅B×A is used implicitly all the time. The Foldable
definition for pairs breaks that symmetry inappropriately.

Cheers,

--Barak.

From ietf-dane at dukhovni.org  Wed Nov 25 20:16:22 2020
From: ietf-dane at dukhovni.org (Viktor Dukhovni)
Date: Wed, 25 Nov 2020 15:16:22 -0500
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,)a)
In-Reply-To: <CANa01BK_KnQ7f2UnqYDgqWkmQ5_K3cMwbDbCzRX94zT9qfv5+w@mail.gmail.com>
References: <mailman.1.1606305601.4495.haskell-cafe@haskell.org>
 <CANa01B+R6r2zQ+EKD-RkntZVhxfioFBgStV47=FcPx4udOprCw@mail.gmail.com>
 <CAK7nUjgBbmOU0rgL7uF_+3Qx+1JxoKSBOyQq3s3uFch8zGLvJg@mail.gmail.com>
 <CANa01BK_KnQ7f2UnqYDgqWkmQ5_K3cMwbDbCzRX94zT9qfv5+w@mail.gmail.com>
Message-ID: <20201125201622.GJ1464@straasha.imrryr.org>

On Wed, Nov 25, 2020 at 07:56:49PM +0000, Barak A. Pearlmutter wrote:

> True. And their use in Arrow is a great example of pairs that do *not*
> work well as instances of Foldable as currently defined. Arrow is
> using pairs as abstract Cartesian products, and the natural
> isomorphism A×B≅B×A is used implicitly all the time. The Foldable
> definition for pairs breaks that symmetry inappropriately.

The "symmetry breaking" is not a result of the perhaps regrettable
Foldable instance, rather it is a basic consequence of the fact that
given:

    data Foo a b = Foo a b

we immediately get a Functor "Foo a :: * -> *" for each a, of which
"(,) a" is but one example.  I find nothing objectionable in the Functor
instance "(,) a" or the Bifunctor instance "(,)".  It is only the
Traversable and Foldable instances of "(,) a" that have the noted
unexpected behaviour.

-- 
    Viktor.

From amindfv at mailbox.org  Wed Nov 25 21:15:18 2020
From: amindfv at mailbox.org (amindfv at mailbox.org)
Date: Wed, 25 Nov 2020 16:15:18 -0500
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,)a)
In-Reply-To: <20201125201622.GJ1464@straasha.imrryr.org>
References: <mailman.1.1606305601.4495.haskell-cafe@haskell.org>
 <CANa01B+R6r2zQ+EKD-RkntZVhxfioFBgStV47=FcPx4udOprCw@mail.gmail.com>
 <CAK7nUjgBbmOU0rgL7uF_+3Qx+1JxoKSBOyQq3s3uFch8zGLvJg@mail.gmail.com>
 <CANa01BK_KnQ7f2UnqYDgqWkmQ5_K3cMwbDbCzRX94zT9qfv5+w@mail.gmail.com>
 <20201125201622.GJ1464@straasha.imrryr.org>
Message-ID: <20201125211518.GA31173@painter.painter>

On Wed, Nov 25, 2020 at 03:16:22PM -0500, Viktor Dukhovni wrote:
> On Wed, Nov 25, 2020 at 07:56:49PM +0000, Barak A. Pearlmutter wrote:
> 
> > True. And their use in Arrow is a great example of pairs that do *not*
> > work well as instances of Foldable as currently defined. Arrow is
> > using pairs as abstract Cartesian products, and the natural
> > isomorphism A×B≅B×A is used implicitly all the time. The Foldable
> > definition for pairs breaks that symmetry inappropriately.
> 
> The "symmetry breaking" is not a result of the perhaps regrettable
> Foldable instance, rather it is a basic consequence of the fact that
> given:
> 
>     data Foo a b = Foo a b
> 
> we immediately get a Functor "Foo a :: * -> *" for each a, of which
> "(,) a" is but one example.  I find nothing objectionable in the Functor
> instance "(,) a" or the Bifunctor instance "(,)".  It is only the
> Traversable and Foldable instances of "(,) a" that have the noted
> unexpected behaviour.

This is almost incidental, though, right? I.e. it's just a result of typeclass "currying" syntax, but it's not hard to imagine a Haskell where similar to how

    foo :: a -> b -> c

gives you both:

    foo a :: b -> c

i.e.

    (\b -> foo a b) :: b -> c

and

    (\a -> foo a b) :: a -> c

we're also allowed to write something like:

    instance Functor (\a -> Foo a b)
    instance Functor (\a -> (a, b))

Mirroring the current (implicit)

    instance Functor (\b -> Foo a b)
    instance Functor (\b -> (a, b))

If that were the case, the instances favoring the last paramater wouldn't seem natural at all, and we'd be sensibly asking on what basis "(+1) <$> (2, 4)" equals (2, 5) but not (3, 4).

Tom


From ietf-dane at dukhovni.org  Wed Nov 25 23:13:10 2020
From: ietf-dane at dukhovni.org (Viktor Dukhovni)
Date: Wed, 25 Nov 2020 18:13:10 -0500
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,)a)
In-Reply-To: <20201125211518.GA31173@painter.painter>
References: <mailman.1.1606305601.4495.haskell-cafe@haskell.org>
 <CANa01B+R6r2zQ+EKD-RkntZVhxfioFBgStV47=FcPx4udOprCw@mail.gmail.com>
 <CAK7nUjgBbmOU0rgL7uF_+3Qx+1JxoKSBOyQq3s3uFch8zGLvJg@mail.gmail.com>
 <CANa01BK_KnQ7f2UnqYDgqWkmQ5_K3cMwbDbCzRX94zT9qfv5+w@mail.gmail.com>
 <20201125201622.GJ1464@straasha.imrryr.org>
 <20201125211518.GA31173@painter.painter>
Message-ID: <20201125231310.GL1464@straasha.imrryr.org>

On Wed, Nov 25, 2020 at 04:15:18PM -0500, amindfv--- via Haskell-Cafe wrote:

> > The "symmetry breaking" is not a result of the perhaps regrettable
> > Foldable instance, rather it is a basic consequence of the fact that
> > given:
> > 
> >     data Foo a b = Foo a b
> > 
> > we immediately get a Functor "Foo a :: * -> *" for each a, of which
> > "(,) a" is but one example.  I find nothing objectionable in the Functor
> > instance "(,) a" or the Bifunctor instance "(,)".  It is only the
> > Traversable and Foldable instances of "(,) a" that have the noted
> > unexpected behaviour.
> 
> This is almost incidental, though, right? I.e. it's just a result of
> typeclass "currying" syntax,

Yes, the last type variable gets the "for free" functor instance.

> but it's not hard to imagine a Haskell where [...]
> 
> we're also allowed to write something like:
> 
>     instance Functor (\a -> Foo a b)
>     instance Functor (\a -> (a, b))
> 
> Mirroring the current (implicit)
> 
>     instance Functor (\b -> Foo a b)
>     instance Functor (\b -> (a, b))
> 
> If that were the case, the instances favoring the last paramater
> wouldn't seem natural at all, and we'd be sensibly asking on what
> basis "(+1) <$> (2, 4)" equals (2, 5) but not (3, 4).

The intent is clear, but ultimately not as useful as one might wish,
since when it comes down to evaluating terms:

    fmap f (x, y)

at most one such instance can match, since the terms don't carry any
information about whether you want to fmap on the left or right.  So
all you'd get to do is flip the bias from right to left.

To avoid the bias we have Bifunctors:

    first :: Bifunctor p => (a -> b) -> p a c -> p b c
    second :: Bifunctor p => (b -> c) -> p a b -> p a c

For selectable bias on 2-tuples, one needs newtypes:

    {-# LANGUAGE FlexibleContexts #-}
    {-# LANGUAGE FlexibleInstances #-}
    {-# LANGUAGE FunctionalDependencies #-}

    import Data.Bifunctor
    import Data.Coerce

    class Coercible c (a,b) => NewPair c a b | c -> a, c -> b where
        toPair :: c -> (a, b)
        toPair = coerce
        {-# INLINE toPair #-}

        fromPair :: (a, b) -> c
        fromPair = coerce
        {-# INLINE fromPair #-}

    -- RPair is redundant, except to avoid Foldable, ... instances
    newtype LPair b a = LPair (a, b) deriving (Eq, Ord, Read, Show)
    newtype RPair a b = RPair (a, b) deriving (Eq, Ord, Read, Show)

    instance NewPair (a, b) a b
    instance NewPair (LPair b a) a b
    instance NewPair (RPair a b) a b

    instance Functor (LPair a) where
        fmap f = fromPair . first f . toPair
    instance Functor (RPair a) where
        fmap f = fromPair . second f . toPair

with the above:

    λ> fmap succ $ LPair (1, 10)
    LPair (2,10)
    λ> fmap succ $ RPair (1, 10)
    RPair (1,11)

-- 
    Viktor.

From twilson at csufresno.edu  Thu Nov 26 00:19:57 2020
From: twilson at csufresno.edu (Todd Wilson)
Date: Wed, 25 Nov 2020 16:19:57 -0800
Subject: [Haskell-cafe] Types of partially instantiated polymorphic
	helper functions
In-Reply-To: <alpine.DEB.2.20.2011250049210.5555@sputnik>
References: <CA+-99oLq1SC2_aoQSYw101vH07CUtiLwbEM8H5eXqdak=0gN-w@mail.gmail.com>
 <af507a6d-aadc-d668-adb2-d31726163a87@well-typed.com>
 <CA+-99oKcKa29=LTGF4DRYb4V-xpcfGabcn9HgubxctvVqwtbEw@mail.gmail.com>
 <20201124233830.GI1464@straasha.imrryr.org>
 <alpine.DEB.2.20.2011250049210.5555@sputnik>
Message-ID: <CA+-99o+=A0iTe=v4RRm3rD3PinBfhz_eZeM8ZoLpGFE4CT8kHg@mail.gmail.com>

Thanks for the additional responses. For the record, in response to

On Tue, Nov 24, 2020 at 3:51 PM Henning Thielemann
<lemming at henning-thielemann.de> wrote:
> An alternative would be to let g be polymorphic but add 'a' as parameter:
>
>    f a bs = g a bs where
>       g :: a -> [b] -> [(a, b)]
>       g = map ((,) a)

this is what I had been doing before -- adding variables that were in
scope as additional arguments to recursive helper functions, even
though they don't change during recursive calls -- just so that I
could give type annotations to helper functions for the purposes of
documentation, since I didn't see any other way. (Of course, my helper
function here is a simple application of `map`, but I was choosing
this minimal example to illustrate something that came up repeatedly
in more complicated situations.) The use of `ScopedTypeVariables`,
though, is a better solution for me, since it allows me to continue my
annotation practice without having to change the code I would
ordinarily write. FWIW, my audience is college students using Haskell
to supplement non-PL classes, and the annotations, perhaps more than
usual, help them understand the code. Since I've already discussed
polymorphism and type variables by that point, the explicit `forall`s
(and language pragmas) are a satisfyingly minimal and easily
explainable intrusion.

Todd Wilson

From amindfv at mailbox.org  Thu Nov 26 00:23:20 2020
From: amindfv at mailbox.org (amindfv at mailbox.org)
Date: Wed, 25 Nov 2020 19:23:20 -0500
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,)a)
In-Reply-To: <20201125231310.GL1464@straasha.imrryr.org>
References: <mailman.1.1606305601.4495.haskell-cafe@haskell.org>
 <CANa01B+R6r2zQ+EKD-RkntZVhxfioFBgStV47=FcPx4udOprCw@mail.gmail.com>
 <CAK7nUjgBbmOU0rgL7uF_+3Qx+1JxoKSBOyQq3s3uFch8zGLvJg@mail.gmail.com>
 <CANa01BK_KnQ7f2UnqYDgqWkmQ5_K3cMwbDbCzRX94zT9qfv5+w@mail.gmail.com>
 <20201125201622.GJ1464@straasha.imrryr.org>
 <20201125211518.GA31173@painter.painter>
 <20201125231310.GL1464@straasha.imrryr.org>
Message-ID: <20201126002320.GA4766@painter.painter>

On Wed, Nov 25, 2020 at 06:13:10PM -0500, Viktor Dukhovni wrote:
> On Wed, Nov 25, 2020 at 04:15:18PM -0500, amindfv--- via Haskell-Cafe wrote:
> 
> > > The "symmetry breaking" is not a result of the perhaps regrettable
> > > Foldable instance, rather it is a basic consequence of the fact that
> > > given:
> > > 
> > >     data Foo a b = Foo a b
> > > 
> > > we immediately get a Functor "Foo a :: * -> *" for each a, of which
> > > "(,) a" is but one example.  I find nothing objectionable in the Functor
> > > instance "(,) a" or the Bifunctor instance "(,)".  It is only the
> > > Traversable and Foldable instances of "(,) a" that have the noted
> > > unexpected behaviour.
> > 
> > This is almost incidental, though, right? I.e. it's just a result of
> > typeclass "currying" syntax,
> 
> Yes, the last type variable gets the "for free" functor instance.
> 
> > but it's not hard to imagine a Haskell where [...]
> > 
> > we're also allowed to write something like:
> > 
> >     instance Functor (\a -> Foo a b)
> >     instance Functor (\a -> (a, b))
> > 
> > Mirroring the current (implicit)
> > 
> >     instance Functor (\b -> Foo a b)
> >     instance Functor (\b -> (a, b))
> > 
> > If that were the case, the instances favoring the last paramater
> > wouldn't seem natural at all, and we'd be sensibly asking on what
> > basis "(+1) <$> (2, 4)" equals (2, 5) but not (3, 4).
> 
> The intent is clear, but ultimately not as useful as one might wish,
> since when it comes down to evaluating terms:
> 
>     fmap f (x, y)
> 
> at most one such instance can match, since the terms don't carry any
> information about whether you want to fmap on the left or right.  So
> all you'd get to do is flip the bias from right to left.
> 

Not sure if we're agreeing or not :-), but this is exactly my point:
The fact that (fmap f (x, y)) == (Control.Arrow.second f (x, y)) seems to only be based, essentially, on the historical accident that in Haskell the last type variable is special w.r.t. typeclass instances.

It's not hard to imagine, in the absence of these instances, Haskell loosening the restriction on creating these types of instances. The restriction is certainly not innate to mathematics or type theory.

My position is against having most of these instances in base, not for switching the bias from right to left.

Tom


From kazu at iij.ad.jp  Thu Nov 26 01:10:12 2020
From: kazu at iij.ad.jp (Kazu Yamamoto (=?iso-2022-jp?B?GyRCOzNLXE9CSScbKEI=?=))
Date: Thu, 26 Nov 2020 10:10:12 +0900 (JST)
Subject: [Haskell-cafe] network v3.1.2.1
Message-ID: <20201126.101012.1048233394485845766.kazu@iij.ad.jp>

Hi cafe,

network v3.1.2.1 has been released. This version is bug-fixes only:

* Increasing base lower bound to 4.9.
  [#473](https://github.com/haskell/network/pull/473)
* Suppressing errors from removeFile in UNIX bind.
  [#478](https://github.com/haskell/network/pull/478)
* Restoring UNIX stub functions on Windows.
  [#489](https://github.com/haskell/network/pull/489)

--Kazu

From ietf-dane at dukhovni.org  Thu Nov 26 04:24:41 2020
From: ietf-dane at dukhovni.org (Viktor Dukhovni)
Date: Wed, 25 Nov 2020 23:24:41 -0500
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,)a)
In-Reply-To: <20201126002320.GA4766@painter.painter>
References: <mailman.1.1606305601.4495.haskell-cafe@haskell.org>
 <CANa01B+R6r2zQ+EKD-RkntZVhxfioFBgStV47=FcPx4udOprCw@mail.gmail.com>
 <CAK7nUjgBbmOU0rgL7uF_+3Qx+1JxoKSBOyQq3s3uFch8zGLvJg@mail.gmail.com>
 <CANa01BK_KnQ7f2UnqYDgqWkmQ5_K3cMwbDbCzRX94zT9qfv5+w@mail.gmail.com>
 <20201125201622.GJ1464@straasha.imrryr.org>
 <20201125211518.GA31173@painter.painter>
 <20201125231310.GL1464@straasha.imrryr.org>
 <20201126002320.GA4766@painter.painter>
Message-ID: <20201126042441.GM1464@straasha.imrryr.org>

On Wed, Nov 25, 2020 at 07:23:20PM -0500, amindfv--- via Haskell-Cafe wrote:

> > The intent is clear, but ultimately not as useful as one might wish,
> > since when it comes down to evaluating terms:
> > 
> >     fmap f (x, y)
> > 
> > at most one such instance can match, since the terms don't carry any
> > information about whether you want to fmap on the left or right.  So
> > all you'd get to do is flip the bias from right to left.
> 
> Not sure if we're agreeing or not :-), but this is exactly my point:

We're not disagreeing. :-)

> The fact that (fmap f (x, y)) == (Control.Arrow.second f (x, y)) seems
> to only be based, essentially, on the historical accident that in
> Haskell the last type variable is special w.r.t. typeclass instances.

Yes, basically, which makes it easy to define Functor and related
instances for the partially applied two parameter type constructor:

    Foo a :: * -> *

and these are somewhat useful, since one then gets to embelish
a general thing with some additional data:
    
        a -> (decorated, a)

and adding the decoration on the left comes with a built-in functor
instance, which, though the left/right choice is a somewhat (but not
entirely) arbitrary choice, does no harm.  No surprising behaviour
arises from the Functor/Applicative/Monad instances for 2-tuples.

Indeed, you probably find it less surprising that with "Either a b" and
"Left a" as the conventional "exception" slot, the Functor instance
transforms "Right b".  The overall approach is consistent in its right
bias, made more convenient through currying of multi-parameter type
constructors.

AFAICT, it is really just the Foldable instance that can lead to
unexpected and behaviour and unnoticed bugs.

> It's not hard to imagine, in the absence of these instances, Haskell
> loosening the restriction on creating these types of instances. The
> restriction is certainly not innate to mathematics or type theory.

Type inference would get more complicated if it would have to consider
all possible slots in each term when searching for the instance head.

> My position is against having most of these instances in base, not for
> switching the bias from right to left.

So you'd like to see a 2-tuple with fewer built-in instances, I'm
sympathetic to the case for not having Traversable/Foldable for
2-tuples, but I don't see a compelling for not having Functor/Monad.

-- 
    Viktor.

From magnus at therning.org  Thu Nov 26 13:12:49 2020
From: magnus at therning.org (Magnus Therning)
Date: Thu, 26 Nov 2020 14:12:49 +0100
Subject: [Haskell-cafe] Amazonka, conduit and sockets not closing
Message-ID: <874klcgt2m.fsf@therning.org>

I've run into a problem with running out of filedescriptors. The
following snippet is a trimmed down version of what I'm doing:

#+begin_src haskell
main :: IO ()
main = do
  awsEnv <- newEnv Discover
  runAWSCond awsEnv $
    sqsSource queueUrl
      .| C.mapC snd
      .| sqsDeleteSink queueUrl
  where
    runAWSCond awsEnv = runResourceT . runAWS awsEnv . within Frankfurt . C.runConduit

sqsSource :: MonadAWS m => T.Text -> C.ConduitT () (T.Text, T.Text) m ()
sqsSource queueUrl = do
  (_, msgs) <- C.lift $ recvSQS queueUrl
  C.yieldMany msgs
  sqsSource queueUrl

sqsDeleteSink :: MonadAWS m => T.Text -> C.ConduitT T.Text o m ()
sqsDeleteSink queueUrl = do
  C.await >>= \case
    Nothing -> pure ()
    Just receiptHandle -> do
      void $ C.lift $ delSQS queueUrl receiptHandle
      sqsDeleteSink queueUrl

recvSQS queueUrl = do
  let rm = receiveMessage queueUrl & rmMaxNumberOfMessages ?~ 10
  rmrs <- send rm
  let status = rmrs ^. rmrsResponseStatus
      msgs = rmrs ^. rmrsMessages & traversed %~ extract
  pure (status, catMaybes msgs)
  where
    extract msg = do
      body <- msg ^. mBody
      rh <- msg ^. mReceiptHandle
      pure (body, rh)

delSQS queueUrl receiptHandle = do
  let dm = deleteMessage queueUrl receiptHandle
  send dm
#+end_src

This works fine for a while, but given a queue with enough messages it will fail
with something like

#+begin_example
TransportError (HttpExceptionRequest Request {
  host                 = "sqs.eu-central-1.amazonaws.com"
  port                 = 443
  secure               = True
  requestHeaders       = [("Host","sqs.eu-central-1.amazonaws.com"),("X-Amz-Date","20201126T101659Z"),("X-Amz-Content-SHA256","2e4bdf20a857a1416f218b1218670cf019ff53268d0adb34fe06402a62f3271d"),("Content-Type","application/x-www-form-urlencoded; charset=utf-8"),("Authorization","<REDACTED>")]
  path                 = "/"
  queryString          = ""
  method               = "POST"
  proxy                = Nothing
  rawBody              = False
  redirectCount        = 0
  responseTimeout      = ResponseTimeoutMicro 70000000
  requestVersion       = HTTP/1.1
}
 (ConnectionFailure Network.Socket.getAddrInfo (called with preferred socket type/protocol: AddrInfo {addrFlags = [AI_ADDRCONFIG], addrFamily = AF_UNSPEC, addrSocketType = Stream, addrProtocol = 0, addrAddress = <assumed to be undefined>, addrCanonName = <assumed to be undefined>}, host name: Just "sqs.eu-central-1.amazonaws.com", service name: Just "443"): does not exist (System error)))
#+end_example

After some detours I found out that it's actually not a network issue, but
rather that the process runs out of filedescriptors. Using =lsof= I can see that
it doesn't seem to close /any/ sockets at all, instead they get stuck in a
=CLOSE_WAIT= state:

#+begin_example
COMMAND    PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
wd-stats 88674 magnus   23u  IPv4 815196      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:60624->52.119.188.213:https (CLOSE_WAIT)
wd-stats 88674 magnus   24u  IPv4 811362      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:43482->52.119.189.184:https (CLOSE_WAIT)
wd-stats 88674 magnus   25u  IPv4 811386      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:60628->52.119.188.213:https (CLOSE_WAIT)
wd-stats 88674 magnus   26u  IPv4 813527      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:43486->52.119.189.184:https (CLOSE_WAIT)
...
#+end_example

Am I using Amazonka and/or Conduit in a way that results in this? How do I should I use them?

Or, is it an issue somewhere "below" my code? What can I do address that?

Thanks for any insights or help
/M

--
Magnus Therning              OpenPGP: 0x927912051716CE39
email: magnus at therning.org
twitter: magthe              http://magnus.therning.org/

Action is the foundational key to all success.
     — Pablo Picasso
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From ietf-dane at dukhovni.org  Thu Nov 26 20:20:22 2020
From: ietf-dane at dukhovni.org (Viktor Dukhovni)
Date: Thu, 26 Nov 2020 15:20:22 -0500
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,)a)
In-Reply-To: <20201126042441.GM1464@straasha.imrryr.org>
References: <mailman.1.1606305601.4495.haskell-cafe@haskell.org>
 <CANa01B+R6r2zQ+EKD-RkntZVhxfioFBgStV47=FcPx4udOprCw@mail.gmail.com>
 <CAK7nUjgBbmOU0rgL7uF_+3Qx+1JxoKSBOyQq3s3uFch8zGLvJg@mail.gmail.com>
 <CANa01BK_KnQ7f2UnqYDgqWkmQ5_K3cMwbDbCzRX94zT9qfv5+w@mail.gmail.com>
 <20201125201622.GJ1464@straasha.imrryr.org>
 <20201125211518.GA31173@painter.painter>
 <20201125231310.GL1464@straasha.imrryr.org>
 <20201126002320.GA4766@painter.painter>
 <20201126042441.GM1464@straasha.imrryr.org>
Message-ID: <20201126202022.GO1464@straasha.imrryr.org>

On Wed, Nov 25, 2020 at 11:24:41PM -0500, Viktor Dukhovni wrote:

> > It's not hard to imagine, in the absence of these instances, Haskell
> > loosening the restriction on creating these types of instances. The
> > restriction is certainly not innate to mathematics or type theory.
> 
> Type inference would get more complicated if it would have to consider
> all possible slots in each term when searching for the instance head.
> 
> > My position is against having most of these instances in base, not for
> > switching the bias from right to left.
> 
> So you'd like to see a 2-tuple with fewer built-in instances, I'm
> sympathetic to the case for not having Traversable/Foldable for
> 2-tuples, but I don't see a compelling for not having Functor/Monad.

Would the attached module be useful to you or anyone else?  It
implements two newtype-wrapped types: 'LP a b' and 'RP a b'.

'LP a b' has a run-time represenation of (and is coercible to) (b, a).
It is a Functor, Applicative and Monad in the left slot of the
underlying 2-tuple.

'RP a b' has a run-time representation of (a, b) and is a Functor,
Applicative and Monad in the right slot of the underlying 2-tuple.

    λ> :t LP (1, "foo")
    LP (1, "foo") :: Num b => OrderedPair 'BL [Char] b
    λ> :t RP (1, "foo")
    RP (1, "foo") :: Num a => OrderedPair 'BR a [Char]

These share the "safe" class instances of (,) from Prelude, but omit
the potentially problematic Foldable (and hence also Traversable).

    λ> fmap succ $ LP (1, 10)
    LP (2,10)
    λ> fmap succ $ RP (1, 10)
    RP (1,11)

The Bifunctor instance is therefore "flipped" in the "LP" case:

    λ> bimap succ pred $ LP (1, 10)
    LP (0,11)
    λ> bimap succ pred $ RP (1, 10)
    RP (2,9)

The class 'LROrder' exports zero-cost coercions to ordinary 2-tuples,
and also conversions to 2-tuples that take/return (a, b) regardless
of the underlying 2-tuple representation.

    λ> toPair $ LP (1, "foo")
    (1,"foo")
    λ> rePair $ LP (1, "foo")
    ("foo",1)
    λ> toPair $ RP (1, "foo")
    (1,"foo")
    λ> rePair $ RP (1, "foo")
    (1,"foo")

Application code can be polymorphic in the 2-tuple order:

    foo :: LROrder o => ((a, b) -> x) -> OrderedPair o a b -> x
    foo f = f . rePair

    bar :: LROrder o => (b -> c) -> OrderedPair o a b -> OrderedPair o a c
    bar f = fmap f

or when desired work with a given order using coercions to extract the
underlying representation for interaction with external libraries.

    foo :: ((b, a) -> x) -> LP a b -> x
    foo f = f . toPair

    bar :: ((a, b) -> x) -> RP a b -> x
    bar f = f . toPair

    baz :: (b -> c) -> ((c, a) -> x) -> LP a b -> x
    baz f g = g . toPair . fmap f

I expect that for most cases the (b, a) representation is not
particularly compelling.  And the order-polymorphism is not needed.  In
other words, the existing "bias" of Functor, Applicative and Monad to
operate on the second element is a natural convention rather than an
obstacle.

-- 
    Viktor.
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From b at chreekat.net  Sat Nov 28 16:41:57 2020
From: b at chreekat.net (Bryan Richter)
Date: Sat, 28 Nov 2020 18:41:57 +0200
Subject: [Haskell-cafe] Amazonka, conduit and sockets not closing
In-Reply-To: <874klcgt2m.fsf@therning.org>
References: <874klcgt2m.fsf@therning.org>
Message-ID: <CAH9BU=xj1=XyEL88m_MdJzx6KcFt2PvnL-0rxxyg85SdGYq82g@mail.gmail.com>

I thought CLOSE_WAIT *is* one of the "closed" states. TCP sockets
stick around for a few minutes after use, right? You may simply be
generating sockets faster than one operating system can handle. Find
some way to reuse existing sockets, perhaps?

On Thu, Nov 26, 2020 at 3:13 PM Magnus Therning <magnus at therning.org> wrote:
>
> I've run into a problem with running out of filedescriptors. The
> following snippet is a trimmed down version of what I'm doing:
>
> #+begin_src haskell
> main :: IO ()
> main = do
>   awsEnv <- newEnv Discover
>   runAWSCond awsEnv $
>     sqsSource queueUrl
>       .| C.mapC snd
>       .| sqsDeleteSink queueUrl
>   where
>     runAWSCond awsEnv = runResourceT . runAWS awsEnv . within Frankfurt . C.runConduit
>
> sqsSource :: MonadAWS m => T.Text -> C.ConduitT () (T.Text, T.Text) m ()
> sqsSource queueUrl = do
>   (_, msgs) <- C.lift $ recvSQS queueUrl
>   C.yieldMany msgs
>   sqsSource queueUrl
>
> sqsDeleteSink :: MonadAWS m => T.Text -> C.ConduitT T.Text o m ()
> sqsDeleteSink queueUrl = do
>   C.await >>= \case
>     Nothing -> pure ()
>     Just receiptHandle -> do
>       void $ C.lift $ delSQS queueUrl receiptHandle
>       sqsDeleteSink queueUrl
>
> recvSQS queueUrl = do
>   let rm = receiveMessage queueUrl & rmMaxNumberOfMessages ?~ 10
>   rmrs <- send rm
>   let status = rmrs ^. rmrsResponseStatus
>       msgs = rmrs ^. rmrsMessages & traversed %~ extract
>   pure (status, catMaybes msgs)
>   where
>     extract msg = do
>       body <- msg ^. mBody
>       rh <- msg ^. mReceiptHandle
>       pure (body, rh)
>
> delSQS queueUrl receiptHandle = do
>   let dm = deleteMessage queueUrl receiptHandle
>   send dm
> #+end_src
>
> This works fine for a while, but given a queue with enough messages it will fail
> with something like
>
> #+begin_example
> TransportError (HttpExceptionRequest Request {
>   host                 = "sqs.eu-central-1.amazonaws.com"
>   port                 = 443
>   secure               = True
>   requestHeaders       = [("Host","sqs.eu-central-1.amazonaws.com"),("X-Amz-Date","20201126T101659Z"),("X-Amz-Content-SHA256","2e4bdf20a857a1416f218b1218670cf019ff53268d0adb34fe06402a62f3271d"),("Content-Type","application/x-www-form-urlencoded; charset=utf-8"),("Authorization","<REDACTED>")]
>   path                 = "/"
>   queryString          = ""
>   method               = "POST"
>   proxy                = Nothing
>   rawBody              = False
>   redirectCount        = 0
>   responseTimeout      = ResponseTimeoutMicro 70000000
>   requestVersion       = HTTP/1.1
> }
>  (ConnectionFailure Network.Socket.getAddrInfo (called with preferred socket type/protocol: AddrInfo {addrFlags = [AI_ADDRCONFIG], addrFamily = AF_UNSPEC, addrSocketType = Stream, addrProtocol = 0, addrAddress = <assumed to be undefined>, addrCanonName = <assumed to be undefined>}, host name: Just "sqs.eu-central-1.amazonaws.com", service name: Just "443"): does not exist (System error)))
> #+end_example
>
> After some detours I found out that it's actually not a network issue, but
> rather that the process runs out of filedescriptors. Using =lsof= I can see that
> it doesn't seem to close /any/ sockets at all, instead they get stuck in a
> =CLOSE_WAIT= state:
>
> #+begin_example
> COMMAND    PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
> wd-stats 88674 magnus   23u  IPv4 815196      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:60624->52.119.188.213:https (CLOSE_WAIT)
> wd-stats 88674 magnus   24u  IPv4 811362      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:43482->52.119.189.184:https (CLOSE_WAIT)
> wd-stats 88674 magnus   25u  IPv4 811386      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:60628->52.119.188.213:https (CLOSE_WAIT)
> wd-stats 88674 magnus   26u  IPv4 813527      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:43486->52.119.189.184:https (CLOSE_WAIT)
> ...
> #+end_example
>
> Am I using Amazonka and/or Conduit in a way that results in this? How do I should I use them?
>
> Or, is it an issue somewhere "below" my code? What can I do address that?
>
> Thanks for any insights or help
> /M
>
> --
> Magnus Therning              OpenPGP: 0x927912051716CE39
> email: magnus at therning.org
> twitter: magthe              http://magnus.therning.org/
>
> Action is the foundational key to all success.
>      — Pablo Picasso
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.

From will.yager at gmail.com  Sat Nov 28 17:42:58 2020
From: will.yager at gmail.com (Will Yager)
Date: Sat, 28 Nov 2020 09:42:58 -0800
Subject: [Haskell-cafe] Amazonka, conduit and sockets not closing
In-Reply-To: <CAH9BU=xj1=XyEL88m_MdJzx6KcFt2PvnL-0rxxyg85SdGYq82g@mail.gmail.com>
References: <CAH9BU=xj1=XyEL88m_MdJzx6KcFt2PvnL-0rxxyg85SdGYq82g@mail.gmail.com>
Message-ID: <EC10FE3C-9419-41CC-B577-51779BE5A155@gmail.com>

Linux has kernel params you can tweak for socket reuse. Also look up SO_REUSEADDR for background. 

> On Nov 28, 2020, at 8:44 AM, Bryan Richter <b at chreekat.net> wrote:
> 
> I thought CLOSE_WAIT *is* one of the "closed" states. TCP sockets
> stick around for a few minutes after use, right? You may simply be
> generating sockets faster than one operating system can handle. Find
> some way to reuse existing sockets, perhaps?
> 
>> On Thu, Nov 26, 2020 at 3:13 PM Magnus Therning <magnus at therning.org> wrote:
>> 
>> I've run into a problem with running out of filedescriptors. The
>> following snippet is a trimmed down version of what I'm doing:
>> 
>> #+begin_src haskell
>> main :: IO ()
>> main = do
>>  awsEnv <- newEnv Discover
>>  runAWSCond awsEnv $
>>    sqsSource queueUrl
>>      .| C.mapC snd
>>      .| sqsDeleteSink queueUrl
>>  where
>>    runAWSCond awsEnv = runResourceT . runAWS awsEnv . within Frankfurt . C.runConduit
>> 
>> sqsSource :: MonadAWS m => T.Text -> C.ConduitT () (T.Text, T.Text) m ()
>> sqsSource queueUrl = do
>>  (_, msgs) <- C.lift $ recvSQS queueUrl
>>  C.yieldMany msgs
>>  sqsSource queueUrl
>> 
>> sqsDeleteSink :: MonadAWS m => T.Text -> C.ConduitT T.Text o m ()
>> sqsDeleteSink queueUrl = do
>>  C.await >>= \case
>>    Nothing -> pure ()
>>    Just receiptHandle -> do
>>      void $ C.lift $ delSQS queueUrl receiptHandle
>>      sqsDeleteSink queueUrl
>> 
>> recvSQS queueUrl = do
>>  let rm = receiveMessage queueUrl & rmMaxNumberOfMessages ?~ 10
>>  rmrs <- send rm
>>  let status = rmrs ^. rmrsResponseStatus
>>      msgs = rmrs ^. rmrsMessages & traversed %~ extract
>>  pure (status, catMaybes msgs)
>>  where
>>    extract msg = do
>>      body <- msg ^. mBody
>>      rh <- msg ^. mReceiptHandle
>>      pure (body, rh)
>> 
>> delSQS queueUrl receiptHandle = do
>>  let dm = deleteMessage queueUrl receiptHandle
>>  send dm
>> #+end_src
>> 
>> This works fine for a while, but given a queue with enough messages it will fail
>> with something like
>> 
>> #+begin_example
>> TransportError (HttpExceptionRequest Request {
>>  host                 = "sqs.eu-central-1.amazonaws.com"
>>  port                 = 443
>>  secure               = True
>>  requestHeaders       = [("Host","sqs.eu-central-1.amazonaws.com"),("X-Amz-Date","20201126T101659Z"),("X-Amz-Content-SHA256","2e4bdf20a857a1416f218b1218670cf019ff53268d0adb34fe06402a62f3271d"),("Content-Type","application/x-www-form-urlencoded; charset=utf-8"),("Authorization","<REDACTED>")]
>>  path                 = "/"
>>  queryString          = ""
>>  method               = "POST"
>>  proxy                = Nothing
>>  rawBody              = False
>>  redirectCount        = 0
>>  responseTimeout      = ResponseTimeoutMicro 70000000
>>  requestVersion       = HTTP/1.1
>> }
>> (ConnectionFailure Network.Socket.getAddrInfo (called with preferred socket type/protocol: AddrInfo {addrFlags = [AI_ADDRCONFIG], addrFamily = AF_UNSPEC, addrSocketType = Stream, addrProtocol = 0, addrAddress = <assumed to be undefined>, addrCanonName = <assumed to be undefined>}, host name: Just "sqs.eu-central-1.amazonaws.com", service name: Just "443"): does not exist (System error)))
>> #+end_example
>> 
>> After some detours I found out that it's actually not a network issue, but
>> rather that the process runs out of filedescriptors. Using =lsof= I can see that
>> it doesn't seem to close /any/ sockets at all, instead they get stuck in a
>> =CLOSE_WAIT= state:
>> 
>> #+begin_example
>> COMMAND    PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
>> wd-stats 88674 magnus   23u  IPv4 815196      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:60624->52.119.188.213:https (CLOSE_WAIT)
>> wd-stats 88674 magnus   24u  IPv4 811362      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:43482->52.119.189.184:https (CLOSE_WAIT)
>> wd-stats 88674 magnus   25u  IPv4 811386      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:60628->52.119.188.213:https (CLOSE_WAIT)
>> wd-stats 88674 magnus   26u  IPv4 813527      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:43486->52.119.189.184:https (CLOSE_WAIT)
>> ...
>> #+end_example
>> 
>> Am I using Amazonka and/or Conduit in a way that results in this? How do I should I use them?
>> 
>> Or, is it an issue somewhere "below" my code? What can I do address that?
>> 
>> Thanks for any insights or help
>> /M
>> 
>> --
>> Magnus Therning              OpenPGP: 0x927912051716CE39
>> email: magnus at therning.org
>> twitter: magthe              http://magnus.therning.org/
>> 
>> Action is the foundational key to all success.
>>     — Pablo Picasso
>> _______________________________________________
>> Haskell-Cafe mailing list
>> To (un)subscribe, modify options or view archives go to:
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>> Only members subscribed via the mailman list are allowed to post.
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.

From ietf-dane at dukhovni.org  Sat Nov 28 18:34:16 2020
From: ietf-dane at dukhovni.org (Viktor Dukhovni)
Date: Sat, 28 Nov 2020 13:34:16 -0500
Subject: [Haskell-cafe] Amazonka, conduit and sockets not closing
In-Reply-To: <874klcgt2m.fsf@therning.org>
References: <874klcgt2m.fsf@therning.org>
Message-ID: <20201128183416.GQ1464@straasha.imrryr.org>

On Thu, Nov 26, 2020 at 02:12:49PM +0100, Magnus Therning wrote:

> After some detours I found out that it's actually not a network issue, but
> rather that the process runs out of filedescriptors. Using =lsof= I can see that
> it doesn't seem to close /any/ sockets at all, instead they get stuck in a
> =CLOSE_WAIT= state:
> 
> #+begin_example
> COMMAND    PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
> wd-stats 88674 magnus   23u  IPv4 815196      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:60624->52.119.188.213:https (CLOSE_WAIT)
> wd-stats 88674 magnus   24u  IPv4 811362      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:43482->52.119.189.184:https (CLOSE_WAIT)
> wd-stats 88674 magnus   25u  IPv4 811386      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:60628->52.119.188.213:https (CLOSE_WAIT)
> wd-stats 88674 magnus   26u  IPv4 813527      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:43486->52.119.189.184:https (CLOSE_WAIT)
> ...
> #+end_example

How many such still open file descriptors did you find?
(If you run "lsof -n -P -i tcp -a -p $pid", it'll produce
the output faster, reporting only sockets).

Contrary to other replies, indeed the sockets above are NOT closed in
your process, otherwise they'd not be associated with a file descriptor
and would just show up in "netstat", but not "lsof" output.

I don't know what happens inside Amazonka, but typically clients doing
many concurrent HTTPS calls employ a TlsManager that maintains a
connection pool, and would avoid opening too many concurrent
connections, but would also keep a limited number of connections open
for more requests.

How many still open connections did you find?  I don't know whether
TlsManager aggregates connections by name or IP address, if the latter,
perhaps (very speculatively, without looking at the underlying code,
...) Amazon's IP address is changing quickly (short or 0 TTL) breaking
the connection pool's per-destination connection limits.  This is a
wild guess, more evidence is needed to make it actually plausible or
rule it out.

-- 
    Viktor.

From amindfv at mailbox.org  Sat Nov 28 21:05:52 2020
From: amindfv at mailbox.org (amindfv at mailbox.org)
Date: Sat, 28 Nov 2020 16:05:52 -0500
Subject: [Haskell-cafe] STM rollback?
Message-ID: <20201128210552.GB20626@painter.painter>

I'd like to be able to give up on an STM transaction: roll back and don't retry.
I've cooked up something with exceptions but it feels a bit icky to use exceptions for something like this - is there a better way?:

    data Rollback = Rollback deriving (Show)
    instance Exception Rollback

    rollback :: STM x
    rollback = throwSTM Rollback

    atomicallyWithRollback :: STM x -> IO (Maybe x)
    atomicallyWithRollback a =
       (Just <$> atomically a)
          `catch` (\Rollback -> pure Nothing)

The alternative I've found is something like:

    otherWay :: STM x -> IO (Maybe x)
    otherWay a =
       atomically $ (Just <$> a) `orElse` pure Nothing

But this turns any "retry" in "a" into a rollback, and I'd like to have the option to do either (retry or rollback).

Thanks,
Tom



From alexander.vershilov at gmail.com  Sat Nov 28 21:14:03 2020
From: alexander.vershilov at gmail.com (Alexander Vershilov)
Date: Sun, 29 Nov 2020 00:14:03 +0300
Subject: [Haskell-cafe] STM rollback?
In-Reply-To: <20201128210552.GB20626@painter.painter>
References: <20201128210552.GB20626@painter.painter>
Message-ID: <1A2C5375-780D-4337-B1F2-E310DEF89C7A@gmail.com>

As far as I understand you can call throwSTM and get desired effect.


—
Alexander Vershilov

> 29 нояб. 2020 г., в 00:07, amindfv--- via Haskell-Cafe <haskell-cafe at haskell.org> написал(а):
> 
> I'd like to be able to give up on an STM transaction: roll back and don't retry.
> I've cooked up something with exceptions but it feels a bit icky to use exceptions for something like this - is there a better way?:
> 
>    data Rollback = Rollback deriving (Show)
>    instance Exception Rollback
> 
>    rollback :: STM x
>    rollback = throwSTM Rollback
> 
>    atomicallyWithRollback :: STM x -> IO (Maybe x)
>    atomicallyWithRollback a =
>       (Just <$> atomically a)
>          `catch` (\Rollback -> pure Nothing)
> 
> The alternative I've found is something like:
> 
>    otherWay :: STM x -> IO (Maybe x)
>    otherWay a =
>       atomically $ (Just <$> a) `orElse` pure Nothing
> 
> But this turns any "retry" in "a" into a rollback, and I'd like to have the option to do either (retry or rollback).
> 
> Thanks,
> Tom
> 
> 
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From fryguybob at gmail.com  Sat Nov 28 23:40:37 2020
From: fryguybob at gmail.com (Ryan Yates)
Date: Sat, 28 Nov 2020 18:40:37 -0500
Subject: [Haskell-cafe] STM rollback?
In-Reply-To: <20201128210552.GB20626@painter.painter>
References: <20201128210552.GB20626@painter.painter>
Message-ID: <CAO27hRpy0kRTwksz2qLtwUfE8ZZDoLstgSSEJVo6dtsAu_btbw@mail.gmail.com>

I think how you want to do this depends on the motivation of why you want
to rollback.  Note that rolling back based on information *inside* the
transaction means that the transaction must be consistent to successfully
rollback.  If you want to trigger rolling back from *outside* the
transaction you can do something like this:

atomicallyWithCancel :: TVar Bool -> STM x -> IO (Maybe x)
atomicallyWithCancel cancel act = atomically ((readTVar cancel >>= check .
not >> return Nothing) `orElse` (Just <$> act))

Note that this still has to have a consistent view of memory to
successfully "cancel", but if it reaches the end of the transaction it will
notice an inconsistent read of the "cancel" tvar and restart the
transaction.  Then it will quickly commit the cancel transaction that only
reads a single TVar and returns Nothing.

Ryan

On Sat, Nov 28, 2020 at 4:07 PM amindfv--- via Haskell-Cafe <
haskell-cafe at haskell.org> wrote:

> I'd like to be able to give up on an STM transaction: roll back and don't
> retry.
> I've cooked up something with exceptions but it feels a bit icky to use
> exceptions for something like this - is there a better way?:
>
>     data Rollback = Rollback deriving (Show)
>     instance Exception Rollback
>
>     rollback :: STM x
>     rollback = throwSTM Rollback
>
>     atomicallyWithRollback :: STM x -> IO (Maybe x)
>     atomicallyWithRollback a =
>        (Just <$> atomically a)
>           `catch` (\Rollback -> pure Nothing)
>
> The alternative I've found is something like:
>
>     otherWay :: STM x -> IO (Maybe x)
>     otherWay a =
>        atomically $ (Just <$> a) `orElse` pure Nothing
>
> But this turns any "retry" in "a" into a rollback, and I'd like to have
> the option to do either (retry or rollback).
>
> Thanks,
> Tom
>
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From magnus at therning.org  Sun Nov 29 09:27:59 2020
From: magnus at therning.org (Magnus Therning)
Date: Sun, 29 Nov 2020 10:27:59 +0100
Subject: [Haskell-cafe] Amazonka, conduit and sockets not closing
In-Reply-To: <20201128183416.GQ1464@straasha.imrryr.org>
References: <874klcgt2m.fsf@therning.org>
 <20201128183416.GQ1464@straasha.imrryr.org>
Message-ID: <87sg8sbjhc.fsf@therning.org>


Viktor Dukhovni <ietf-dane at dukhovni.org> writes:

> On Thu, Nov 26, 2020 at 02:12:49PM +0100, Magnus Therning wrote:
>
>> After some detours I found out that it's actually not a network issue, but
>> rather that the process runs out of filedescriptors. Using =lsof= I can see that
>> it doesn't seem to close /any/ sockets at all, instead they get stuck in a
>> =CLOSE_WAIT= state:
>>
>> #+begin_example
>> COMMAND    PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
>> wd-stats 88674 magnus   23u  IPv4 815196      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:60624->52.119.188.213:https (CLOSE_WAIT)
>> wd-stats 88674 magnus   24u  IPv4 811362      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:43482->52.119.189.184:https (CLOSE_WAIT)
>> wd-stats 88674 magnus   25u  IPv4 811386      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:60628->52.119.188.213:https (CLOSE_WAIT)
>> wd-stats 88674 magnus   26u  IPv4 813527      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:43486->52.119.189.184:https (CLOSE_WAIT)
>> ...
>> #+end_example
>
> How many such still open file descriptors did you find?

Hundreds of them.

> (If you run "lsof -n -P -i tcp -a -p $pid", it'll produce
> the output faster, reporting only sockets).
>
> Contrary to other replies, indeed the sockets above are NOT closed in
> your process, otherwise they'd not be associated with a file
> descriptor and would just show up in "netstat", but not "lsof" output.
>
> I don't know what happens inside Amazonka, but typically clients doing
> many concurrent HTTPS calls employ a TlsManager that maintains a
> connection pool, and would avoid opening too many concurrent
> connections, but would also keep a limited number of connections open
> for more requests.

After I reported it to the Amazonka project[1] I found out that it most
likely is a known issue[2].

I have still to confirm that the fix for [2] solves the issue I'm
seeing.

[1]: https://github.com/brendanhay/amazonka/issues/608
[2]: https://github.com/brendanhay/amazonka/issues/490

/M

--
Magnus Therning              OpenPGP: 0x927912051716CE39
email: magnus at therning.org
twitter: magthe              http://magnus.therning.org/

I am always doing that which I cannot do, in order that I may learn
how to do it.
     — Pablo Picasso
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From tonymorris at gmail.com  Mon Nov 30 04:29:22 2020
From: tonymorris at gmail.com (Tony Morris)
Date: Mon, 30 Nov 2020 14:29:22 +1000
Subject: [Haskell-cafe] Textbook example of instance Foldable ((,) a)
In-Reply-To: <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
References: <b1efb440-5188-d9de-7774-c444c650c583@htwk-leipzig.de>
 <CANBN=mvRjQ9a8hnYRKZTkmqcuufVNKZ-OroHAgk-s8UDjZeLpg@mail.gmail.com>
 <874klg6rtx.fsf@uibk.ac.at> <alpine.DEB.2.20.2011231608030.5933@sputnik>
 <87wnyc5cba.fsf@gmail.com>
 <CABhTcUsog=9z+iFLHNXSPMNiq6dAnkkJ8spCEBespac3_YUNsA@mail.gmail.com>
 <CANBN=msRHPrs0e=zfan4fpbhHM9qVz-VkWzqgD-AQLucC59tUQ@mail.gmail.com>
Message-ID: <5405a232-bc9f-c970-67e5-14374e6cf2b2@gmail.com>

Yes.

On 11/24/20 6:18 AM, Sven Panne wrote:
> but is this really what comes to your mind first?

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From compl.yue at icloud.com  Mon Nov 30 06:21:29 2020
From: compl.yue at icloud.com (YueCompl)
Date: Mon, 30 Nov 2020 14:21:29 +0800
Subject: [Haskell-cafe] STM rollback?
In-Reply-To: <20201128210552.GB20626@painter.painter>
References: <20201128210552.GB20626@painter.painter>
Message-ID: <651D1B93-9322-4B7A-8CE2-CE9F0BA907D9@icloud.com>

The exception based solution is the best as far as I can tell for now (But I'm not authoritative of course). Maybe a dedicated `Rollback` algebraic effect and its respective handler would feel less "icky"? But the machinery is not generally available yet, and maybe an algebraic effects based solution will be overkill taking the ergonomic cost it'll impose, even if practically doable?

Regards,
Compl


> On 2020-11-29, at 05:05, amindfv--- via Haskell-Cafe <haskell-cafe at haskell.org> wrote:
> 
> I'd like to be able to give up on an STM transaction: roll back and don't retry.
> I've cooked up something with exceptions but it feels a bit icky to use exceptions for something like this - is there a better way?:
> 
>    data Rollback = Rollback deriving (Show)
>    instance Exception Rollback
> 
>    rollback :: STM x
>    rollback = throwSTM Rollback
> 
>    atomicallyWithRollback :: STM x -> IO (Maybe x)
>    atomicallyWithRollback a =
>       (Just <$> atomically a)
>          `catch` (\Rollback -> pure Nothing)
> 
> The alternative I've found is something like:
> 
>    otherWay :: STM x -> IO (Maybe x)
>    otherWay a =
>       atomically $ (Just <$> a) `orElse` pure Nothing
> 
> But this turns any "retry" in "a" into a rollback, and I'd like to have the option to do either (retry or rollback).
> 
> Thanks,
> Tom
> 
> 
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.


From jo at durchholz.org  Mon Nov 30 08:45:33 2020
From: jo at durchholz.org (Joachim Durchholz)
Date: Mon, 30 Nov 2020 09:45:33 +0100
Subject: [Haskell-cafe] STM rollback?
In-Reply-To: <20201128210552.GB20626@painter.painter>
References: <20201128210552.GB20626@painter.painter>
Message-ID: <5292b95a-e477-1cf4-deee-4605c8296e90@durchholz.org>

 From a contract design perspective, rolling back means that an 
operation failed and had to be undone. (If everything was fine, you 
wouldn't want to rollback, wouldn't you?)

So if rollback is the reaction to some failure, then triggering it via 
an exception is the Right Thing To Do, actually.
Oh, and you always want to rollback if there's an exception somewhere.

Now that contract thing warrants a few more words.
Yes, you can word your contracts so that they include failure. It's just 
that they get more complicated. Usually so much more complicated that 
it's not worth it.
Also, you want any exception (i.e. breach of contract) to go into a 
rollback. Now in Haskell, rolling back means just abandoning the 
computation since things aren't mutable and there is no state that you 
need to restore. Technically, not even in STM - so there *is* reason to 
make the rollback non-exceptional here: One could argue that STM is 
*supposed* to include the rollback in the contract.
In the end, it depends on your use case: Do you want the rollback in the 
contract or not?

Now for STM itself, yeah using an exception to trigger a rollback is a 
bit hacky.
OTOH it works.
OT3H it might be a good idea to have a rollback function for STM. 
Technically it would just trigger the same exception, but it would 
indicate that the rollback is part of the contract.
OT4H throwing Rollback is essentially an indicator of non-failure 
rollback (otherwise you'd be throwing whatever exception is appropriate, 
or get aborted by some library functionality that throws an exception).

Regards,
Jo

Am 28.11.20 um 22:05 schrieb amindfv--- via Haskell-Cafe:
> I'd like to be able to give up on an STM transaction: roll back and don't retry.
> I've cooked up something with exceptions but it feels a bit icky to use exceptions for something like this - is there a better way?:
> 
>      data Rollback = Rollback deriving (Show)
>      instance Exception Rollback
> 
>      rollback :: STM x
>      rollback = throwSTM Rollback
> 
>      atomicallyWithRollback :: STM x -> IO (Maybe x)
>      atomicallyWithRollback a =
>         (Just <$> atomically a)
>            `catch` (\Rollback -> pure Nothing)
> 
> The alternative I've found is something like:
> 
>      otherWay :: STM x -> IO (Maybe x)
>      otherWay a =
>         atomically $ (Just <$> a) `orElse` pure Nothing
> 
> But this turns any "retry" in "a" into a rollback, and I'd like to have the option to do either (retry or rollback).
> 
> Thanks,
> Tom
> 
> 
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
> 


From gueven.bay at googlemail.com  Mon Nov 30 20:34:26 2020
From: gueven.bay at googlemail.com (Gueven Bay)
Date: Mon, 30 Nov 2020 21:34:26 +0100
Subject: [Haskell-cafe] What features should an (fictitious) IDE for Haskell
	have?
Message-ID: <CAHonXRBYtyRtnWnw1Ah7WpKPNOJ86N728mgErs8gXUbL8atrxg@mail.gmail.com>

Greetings,

Imagine that you can decide what functionality and features an
Integrated Development Environment for Haskell should get. You can
make this IDE with your wishlist similar in power as other IDEs for
Java for example.

Now list as many features as you can, what would make the life of a
Haskell developer as comfortable as possible!?

I am dying to know how this list of features at the end (of this
thread) will look like.

From alan.zimm at gmail.com  Mon Nov 30 20:46:39 2020
From: alan.zimm at gmail.com (Alan & Kim Zimmerman)
Date: Mon, 30 Nov 2020 20:46:39 +0000
Subject: [Haskell-cafe] What features should an (fictitious) IDE for
 Haskell have?
In-Reply-To: <CAHonXRBYtyRtnWnw1Ah7WpKPNOJ86N728mgErs8gXUbL8atrxg@mail.gmail.com>
References: <CAHonXRBYtyRtnWnw1Ah7WpKPNOJ86N728mgErs8gXUbL8atrxg@mail.gmail.com>
Message-ID: <CANma=H9U+16Xs=Y2gw08qCTK+EkzBhssgGyGEFo3-qVjRXWw_A@mail.gmail.com>

I would want to see moldable development[1] style search and visualisation.

Or something like [2]

Alan

[1] https://gtoolkit.com/
[2]
https://2020.splashcon.org/details/splash-2020-oopsla/98/Adding-Interactive-Visual-Syntax-to-Textual-Code


On Mon, 30 Nov 2020 at 20:35, Gueven Bay via Haskell-Cafe <
haskell-cafe at haskell.org> wrote:

> Greetings,
>
> Imagine that you can decide what functionality and features an
> Integrated Development Environment for Haskell should get. You can
> make this IDE with your wishlist similar in power as other IDEs for
> Java for example.
>
> Now list as many features as you can, what would make the life of a
> Haskell developer as comfortable as possible!?
>
> I am dying to know how this list of features at the end (of this
> thread) will look like.
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
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From tikhon at jelv.is  Mon Nov 30 21:25:06 2020
From: tikhon at jelv.is (Tikhon Jelvis)
Date: Mon, 30 Nov 2020 13:25:06 -0800
Subject: [Haskell-cafe] What features should an (fictitious) IDE for
 Haskell have?
In-Reply-To: <CANma=H9U+16Xs=Y2gw08qCTK+EkzBhssgGyGEFo3-qVjRXWw_A@mail.gmail.com>
References: <CAHonXRBYtyRtnWnw1Ah7WpKPNOJ86N728mgErs8gXUbL8atrxg@mail.gmail.com>
 <CANma=H9U+16Xs=Y2gw08qCTK+EkzBhssgGyGEFo3-qVjRXWw_A@mail.gmail.com>
Message-ID: <CAJN5CVKLJHODzEizhf6qL8RKQmENGcr8T4wrQDgWW1kZfzRtiQ@mail.gmail.com>

Biggest feature I want is automated refactoring.

Changing a type definition and getting a bunch of errors to fix is one of
the defining features of Haskell as a development experience—but the
changes themselves are still pretty manual, and in larger codebases, this
quickly gets painful. I would love a system where I make a change, get a
bunch of errors and as much of the refactoring as possible is done for me
automatically. This would include traditional refactorings like renaming
functions and constructors, but it would also include more Haskell-specific
refactorings, potentially with some amount of interactiveness. One example
I ran into recently: I added a field to a constructor that was used pretty
widely in my code, especially in lots of tests, and I had to manually
update each pattern using that constructor to disregard the new field and
add a default value (an empty string, in this case) everywhere the
constructor was used to build a value. This was really tedious to do, and
seems systematic enough that it could have been fully automated. In other
scenarios, I would want my editor to cycle me through each location that
needs to update and give me an automated suggestion I can accept or reject
so that I could do a first pass quickly and only spend time on cases that
require more manual intervention.

I have not used any Haskell refactoring tools yet, so I am not sure what
exists today. Google around now, it looks like Facebook's retrie[1] project
might be expressive enough to do the heavy lifting for a tool like this, so
perhaps we just need a friendly frontend for it.

[1]: https://github.com/facebookincubator/retrie

On Mon, Nov 30, 2020 at 12:49 PM Alan & Kim Zimmerman <alan.zimm at gmail.com>
wrote:

> I would want to see moldable development[1] style search and visualisation.
>
> Or something like [2]
>
> Alan
>
> [1] https://gtoolkit.com/
> [2]
> https://2020.splashcon.org/details/splash-2020-oopsla/98/Adding-Interactive-Visual-Syntax-to-Textual-Code
>
>
> On Mon, 30 Nov 2020 at 20:35, Gueven Bay via Haskell-Cafe <
> haskell-cafe at haskell.org> wrote:
>
>> Greetings,
>>
>> Imagine that you can decide what functionality and features an
>> Integrated Development Environment for Haskell should get. You can
>> make this IDE with your wishlist similar in power as other IDEs for
>> Java for example.
>>
>> Now list as many features as you can, what would make the life of a
>> Haskell developer as comfortable as possible!?
>>
>> I am dying to know how this list of features at the end (of this
>> thread) will look like.
>> _______________________________________________
>> Haskell-Cafe mailing list
>> To (un)subscribe, modify options or view archives go to:
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>> Only members subscribed via the mailman list are allowed to post.
>
> _______________________________________________
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From lemming at henning-thielemann.de  Mon Nov 30 21:40:49 2020
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Mon, 30 Nov 2020 22:40:49 +0100 (CET)
Subject: [Haskell-cafe] What features should an (fictitious) IDE for
 Haskell have?
In-Reply-To: <CAJN5CVKLJHODzEizhf6qL8RKQmENGcr8T4wrQDgWW1kZfzRtiQ@mail.gmail.com>
References: <CAHonXRBYtyRtnWnw1Ah7WpKPNOJ86N728mgErs8gXUbL8atrxg@mail.gmail.com>
 <CANma=H9U+16Xs=Y2gw08qCTK+EkzBhssgGyGEFo3-qVjRXWw_A@mail.gmail.com>
 <CAJN5CVKLJHODzEizhf6qL8RKQmENGcr8T4wrQDgWW1kZfzRtiQ@mail.gmail.com>
Message-ID: <alpine.DEB.2.20.2011302238040.7188@sputnik>


On Mon, 30 Nov 2020, Tikhon Jelvis wrote:

> Biggest feature I want is automated refactoring.

Any such refactoring tool would require a (configurable) formatting and 
indentation tool, because even simple search&replace will break your 
layout. Thus, a good code formatter would be an even more important 
feature of the IDE.

From alan.zimm at gmail.com  Mon Nov 30 22:26:44 2020
From: alan.zimm at gmail.com (Alan & Kim Zimmerman)
Date: Mon, 30 Nov 2020 22:26:44 +0000
Subject: [Haskell-cafe] What features should an (fictitious) IDE for
 Haskell have?
In-Reply-To: <alpine.DEB.2.20.2011302238040.7188@sputnik>
References: <CAHonXRBYtyRtnWnw1Ah7WpKPNOJ86N728mgErs8gXUbL8atrxg@mail.gmail.com>
 <CANma=H9U+16Xs=Y2gw08qCTK+EkzBhssgGyGEFo3-qVjRXWw_A@mail.gmail.com>
 <CAJN5CVKLJHODzEizhf6qL8RKQmENGcr8T4wrQDgWW1kZfzRtiQ@mail.gmail.com>
 <alpine.DEB.2.20.2011302238040.7188@sputnik>
Message-ID: <CANma=H9+1eA8zH3meuqqP7vP-QFst3jcO-C=tDc7wN7yU2-ACw@mail.gmail.com>

On Mon, 30 Nov 2020 at 21:42, Henning Thielemann <
lemming at henning-thielemann.de> wrote:

>
> On Mon, 30 Nov 2020, Tikhon Jelvis wrote:
>
> > Biggest feature I want is automated refactoring.
>
> Any such refactoring tool would require a (configurable) formatting and
> indentation tool, because even simple search&replace will break your
> layout. Thus, a good code formatter would be an even more important
> feature of the IDE.
>

The ghc-exactprint library (as used in retrie, hlint refactors and HaRe)
makes it so you can change the AST in a refactoring and preserve
formatting/layout in the result.

Alan
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