Proposal: Add singleton function to Data.List module

Thu Aug 22 12:11:21 UTC 2019

We also use the money face regularly in our code bases, but I think it's
only because the singleton function for lists is not already defined. Every
time I see/use it I wince a little.

Some devs I know will go to lengths to avoid an extra import line. So you
often see 'maybe x id' instead of 'fromMaybe x' and 'flip traverse' instead
of 'for'.

No other containers are in Prelude and must have their APIs imported
qualified. So they don't suffer from this bias against imports.

In any code base the defines it's own idioms, like singleton on lists, you
have to imagine that what's obviously on Hackage and what is proprietary
will not get the same level of commitment.

P.S. Based on arguments against non-fundanental combinators, I suppose we
should remove 'fromMaybe' and 'for' since they are not fundamental?

This debate is definitely more ideological than I think anyone quite
realized at first. At the very least, having the CLC's position clearly
documented might help in the future.

On Thu, Aug 22, 2019, 7:12 AM Malcolm Wallace via Libraries <
libraries at haskell.org> wrote:

> I have some data to contribute, from our proprietary codebase of some
> 4MLoC.  We are perhaps unusual in having the singleton function on lists
> already for 10 years, so it is easy to do a comparison of the frequency of
> use.
>
> The robot monkey (:[]) has 378 uses.
> Monkey with a space (: []) has 36 uses.
> The list singleton function has 18 uses.
>
> We also have many other singleton functions at more than 20 different
> types (vector, tuple, map, set, interval, relation, dict, expression, etc),
> totalling 1893 uses, so the concept/vocabulary is pretty well-known.
>
> In addition, I counted the number of direct constructions of lists that
> use :[] unparenthesised, i.e like x:y:[], and there are 489.
>
> I find it interesting that given the choice of “singleton” vs direct
> construction or a partially applied operator, our devs seem to prefer the
> brevity and naturality of the colon.
>
> Regards,
>     Malcolm
>
> > On 21 Aug 2019, at 06:31, George Wilson <george at wils.online> wrote:
> >
> > Hi Taylor,
> >
> > I'm on the Core Libraries Committee. Thank you for your proposal.
> > Regarding the +-1 messages in this thread, they are useful to gauge
> > community opinion, but they are not votes because the libraries
> > process is not determined by a vote.
> >
> > Despite seeming innocuous, the proposed change requires careful
> > consideration: Data.List is specified by the Haskell Report, so adding
> > this function would affect the report.
> > While simple changes to base are typically handled directly by one of
> > base's maintainers, this change is report-affecting, so it is
> > "controversial" (as defined in [1]). Hence the CLC is discussing the
> > proposed change amongst ourselves before a maintainer makes their
> > decision.
> >
> > [1] https://wiki.haskell.org/Library_submissions
> >
> > Cheers,
> > George
> >
> >
> >
> >
> >
> >> On Tue, 20 Aug 2019 at 11:24, Taylor Fausak <taylor at fausak.me> wrote:
> >>
> >> It has been a week since I submitted my proposal. During that time, 28
> people voted, with 16 expressing approval and 12 expressing disapproval. To
> everyone that voted so far: Thank you! You made for interesting discussion.
> >>
> >> I still feel that Haskell would be improved by the addition of a
> `singleton` function to the `Data.List` module. (And also
> `Data.List.NonEmpty`, even though that wasn't part of my original
> proposal.) I would be happy to open a merge request adding code, tests, and
> documentation.
> >>
> >> I haven't done so yet because I don't know what the next steps are. Can
> someone from the CLC tell me how an official approval or rejection can be
> reached, and how long that might take? Thanks!
> >>
> >> On Mon, Aug 19, 2019, at 6:39 AM, Helmut Schmidt wrote:
> >>
> >>
> >> Andreas, you seem to be mistaken there'd only be one container API? But
> there's several container APIs besides "Data.Set" which provide some
> collection of elements!
> >>
> >>
> https://hackage.haskell.org/package/dlist-0.8.0.7/docs/Data-DList.html#v:cons
> >>
> >>
> https://hackage.haskell.org/package/dlist-0.8.0.7/docs/Data-DList.html#v:append
> >>
> >>
> >>
> >>
> >>
> https://hackage.haskell.org/package/text-1.2.4.0/docs/Data-Text.html#v:cons
> >>
> >>
> https://hackage.haskell.org/package/text-1.2.4.0/docs/Data-Text.html#v:append
> >>
> >>
> http://hackage.haskell.org/package/vector-0.12.0.3/docs/Data-Vector.html#v:cons
> >>
> >>
> https://hackage.haskell.org/package/bytestring-0.10.10.0/docs/Data-ByteString.html#v:cons
> >>
> >>
> https://hackage.haskell.org/package/bytestring-0.10.10.0/docs/Data-ByteString.html#v:append
> >>
> >> Am Mo., 19. Aug. 2019 um 08:16 Uhr schrieb Andreas Abel <
> andreas.abel at ifi.lmu.de>:
> >>
> >> Helmut, do you actually know the container APIs?
> >>
> >> Show me cons and append in Data.Set!
> >>
> >>> On 2019-08-18 19:40, Helmut Schmidt wrote:
> >>>
> >>>
> >>> Am So., 18. Aug. 2019 um 17:17 Uhr schrieb Oliver Charles
> >>> <ollie at ocharles.org.uk <mailto:ollie at ocharles.org.uk>>:
> >>>
> >>>    On Sun, 18 Aug 2019, 5:47 pm Helmut Schmidt,
> >>>    <helmut.schmidt.4711 at gmail.com
> >>>    <mailto:helmut.schmidt.4711 at gmail.com>> wrote:
> >>>
> >>>
> >>>        All these philosophical arguments calling for "consistency" with
> >>>        the container APIs or that function need words for the human
> >>>        mind to comprehend seem short-sighted to me. If we were
> >>>        consistent about the proposal itself we'd also demand to add
> >>>
> >>>           cons = (:)
> >>>
> >>>           empty = []
> >>>
> >>>           toList = id
> >>>
> >>>           fromList = id
> >>>
> >>>
> >>>    I honestly have no problem with any of these.
> >>>
> >>>
> >>> I forgot
> >>>
> >>>     append = (++)
> >>>
> >>> We also need to address another elephant in the room... those pesky
> >>> tuples and their special privileged non-wordy syntax!
> >>>
> >>>    pair = (,)
> >>>
> >>>    triple = (,,)
> >>>
> >>>    quadruple = (,,,)
> >>>
> >>>    quituple = (,,,,)
> >>>
> >>>    sextuple = (,,,,,)
> >>>
> >>>    septuble = (,,,,,,)
> >>>
> >>>    octuple = (,,,,,,,)
> >>>
> >>> If Haskell were invented in this century's EU Haskell source code would
> >>> be littered with €s instead of $s but then again I wonder why £ wasn't
> >>> picked. But I digress. We can kill two birds with one stone here:
> >>>
> >>>    apply = ($)
> >>>
> >>>    strictApply = ($!)
> >>>
> >>>    compose = (.)
> >>>
> >>>
> >>> It's fun to imagine how code using those definitions would like! But
> >>> it's still a -1 for me, sorry!
> >>>
> >>>
> >>>
> >>>
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> >>>
> >>
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