From traqueofziche at gmail.com  Tue Sep  3 08:52:59 2019
From: traqueofziche at gmail.com (=?UTF-8?B?6bKN5Yev5paH?=)
Date: Tue, 3 Sep 2019 01:52:59 -0700
Subject: [Haskell-beginners] how to convert an array of foreignPtr a
	into a list of Ptr a
In-Reply-To: <mailman.5.1566907202.18314.beginners@haskell.org>
References: <mailman.5.1566907202.18314.beginners@haskell.org>
Message-ID: <CAMjcG+Ex5p5Ccf610pgB0o3WjbiOjiFwH73g7T1bCboWjZ29jw@mail.gmail.com>

Hi Frederic,

I tried writing my thoughts on your question in this gist here:
https://gist.github.com/darcykimball/74dd7973b2dbad22b7091135a3b9d472.
There's probably much more to it than what I wrote, but I'm figuring that
stuff out the more I think about it. I'll try to add more when I'm
convinced I get it.

Best,

Kevin

On Tue, Aug 27, 2019 at 5:56 AM <beginners-request at haskell.org> wrote:

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>    1.  how to convert an array of foreignPtr a into a   list of Ptr a
>       (PICCA Frederic-Emmanuel)
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> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 27 Aug 2019 07:19:25 +0000
> From: PICCA Frederic-Emmanuel
>         <frederic-emmanuel.picca at synchrotron-soleil.fr>
> To: "The Haskell-Beginners Mailing List - Discussion of primarily
>         beginner-level topics related to Haskell" <beginners at haskell.org>
> Subject: [Haskell-beginners] how to convert an array of foreignPtr a
>         into a  list of Ptr a
> Message-ID:
>         <
> A2A20EC3B8560D408356CAC2FC148E53016CF535AB at SUN-DAG3.synchrotron-soleil.fr>
>
> Content-Type: text/plain; charset="us-ascii"
>
> Hello, I am writing some code whcih use FFI.
>
> one of my C functions has an array of pointer has imput
>
> extern HklBinocularsCube *hkl_binoculars_cube_new(int32_t n_spaces,
>
>  const HklBinocularsSpace **spaces);
>
>
> from Haskell, I have a list of ForeignPtr
> so my question how can I have something like withForeignPtr for an array
> of ForeignPtr
>
> [ForeignPtr a] -> ([Ptr a] -> IO b) -> IO b
>
> Thanks for your help.
>
> Frederic
>
> ------------------------------
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> End of Beginners Digest, Vol 134, Issue 4
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From frederic-emmanuel.picca at synchrotron-soleil.fr  Tue Sep  3 09:01:21 2019
From: frederic-emmanuel.picca at synchrotron-soleil.fr (PICCA Frederic-Emmanuel)
Date: Tue, 3 Sep 2019 09:01:21 +0000
Subject: [Haskell-beginners] how to convert an array of foreignPtr
 a	into a list of Ptr a
In-Reply-To: <CAMjcG+Ex5p5Ccf610pgB0o3WjbiOjiFwH73g7T1bCboWjZ29jw@mail.gmail.com>
References: <mailman.5.1566907202.18314.beginners@haskell.org>,
 <CAMjcG+Ex5p5Ccf610pgB0o3WjbiOjiFwH73g7T1bCboWjZ29jw@mail.gmail.com>
Message-ID: <A2A20EC3B8560D408356CAC2FC148E53016CF58065@SUN-DAG3.synchrotron-soleil.fr>

thanks you very much.

it is a very helpfull explaination.

Cheers,

Frederic

From jcg.sturdy at gmail.com  Thu Sep 26 13:53:23 2019
From: jcg.sturdy at gmail.com (John Sturdy)
Date: Thu, 26 Sep 2019 14:53:23 +0100
Subject: [Haskell-beginners] Import errors from a very simple program
Message-ID: <CAFJf9KNhVy5QpYyhM0XTnOKQzoZeOShFkCETmTr_kHqkcqqBFw@mail.gmail.com>

Hi,

I'm right at the start of learning Haskell, and I decided to jump from
reading LYAH to writing a simple real-world program.

It's based very closely on
https://github.com/haskell-hvr/cassava/blob/master/examples/NamedBasedGeneric.hs
(I removed the bit that constructs the test file, as I already have a
file), and I've done "cabal install cassava", first as root, and then when
I first go the error, as myself using the sandbox (which didn't change the
output).  I first tried this with running ghc directly, and then followed
the instructions on https://wiki.haskell.org/How_to_write_a_Haskell_program,
and all these get the same errors:

Main.hs:4:1: error:
    Could not find module ‘Data.Csv’
    Locations searched:
      Data/Csv.hs
      Data/Csv.lhs
      Data/Csv.hsig
      Data/Csv.lhsig
  |
4 | import Data.Csv
  | ^^^^^^^^^^^^^^^

Main.hs:6:1: error:
    Could not find module ‘Data.Vector’
    Perhaps you meant Data.Functor (from base-4.11.1.0)
    Locations searched:
      Data/Vector.hs
      Data/Vector.lhs
      Data/Vector.hsig
      Data/Vector.lhsig
  |
6 | import qualified Data.Vector as V
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I don't understand the connection between the name "cassava" and
"Data/Csv", although looking around in the directories that have been
produced, I see that Data/Csv is within the cassava directories.   I'd like
not only to know how to fix this,  but also a pointer for what I should
look at to understand what is going on.

This is on a Debian system.

thanks,

__John (completely new to Haskell, experienced in C, Lisp, Python and
others, if that helps to pitch the level of answers)
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From fa-ml at ariis.it  Thu Sep 26 14:15:40 2019
From: fa-ml at ariis.it (Francesco Ariis)
Date: Thu, 26 Sep 2019 16:15:40 +0200
Subject: [Haskell-beginners] Import errors from a very simple program
In-Reply-To: <CAFJf9KNhVy5QpYyhM0XTnOKQzoZeOShFkCETmTr_kHqkcqqBFw@mail.gmail.com>
References: <CAFJf9KNhVy5QpYyhM0XTnOKQzoZeOShFkCETmTr_kHqkcqqBFw@mail.gmail.com>
Message-ID: <20190926141540.lajv5celof4jh437@x60s.casa>

Hello John,

On Thu, Sep 26, 2019 at 02:53:23PM +0100, John Sturdy wrote:
> Hi,
> 
> I'm right at the start of learning Haskell, and I decided to jump from
> reading LYAH to writing a simple real-world program.
> 
> It's based very closely on
> https://github.com/haskell-hvr/cassava/blob/master/examples/NamedBasedGeneric.hs

Cabalising a small project is one way to do it (and a useful skill
to learn, too):

    cd ~/somefolder
    wget -O Main.hs https://raw.githubusercontent.com/haskell-hvr/cassava/master/examples/NamedBasedGeneric.hs
    cabal init --is-executable --dependency=base --dependency=bytestring --dependency=vector --dependency=text --dependency=cassava
        # many questions! There is a non-interactive option.
    cabal new-repl
        # ghci repl for your project
    λ> main

Bingo!
Read the generated .cabal file to learn more on how it works
Does this help?
-F

From daniel.trstenjak at gmail.com  Thu Sep 26 14:18:14 2019
From: daniel.trstenjak at gmail.com (Daniel Trstenjak)
Date: Thu, 26 Sep 2019 16:18:14 +0200
Subject: [Haskell-beginners] Import errors from a very simple program
In-Reply-To: <CAFJf9KNhVy5QpYyhM0XTnOKQzoZeOShFkCETmTr_kHqkcqqBFw@mail.gmail.com>
References: <CAFJf9KNhVy5QpYyhM0XTnOKQzoZeOShFkCETmTr_kHqkcqqBFw@mail.gmail.com>
Message-ID: <20190926141814.GA24606@octa>

Hi John,

if I'm understanding you correctly, you're installing packages by hand
with 'cabal install' and then calling 'ghc' by hand for your source file.

'ghc' won't automatically use the packages you've installed with 'cabal install',
but you've to add them to the 'ghc' call. Your compile error seems to indicate,
that the 'cassava' and 'vector' packages haven't been given to the 'ghc' call.

But most likely it isn't worth the hassle doing this and it is a lot
easier to just create a default cabal file with 'cabal init'. Then you
can add the 'cassava' and 'vector' packages as dependencies and build
the packages and your source file with 'cabal new-build'.

Greetings,
Daniel

From jcg.sturdy at gmail.com  Thu Sep 26 14:26:22 2019
From: jcg.sturdy at gmail.com (John Sturdy)
Date: Thu, 26 Sep 2019 15:26:22 +0100
Subject: [Haskell-beginners] Import errors from a very simple program
In-Reply-To: <20190926141814.GA24606@octa>
References: <CAFJf9KNhVy5QpYyhM0XTnOKQzoZeOShFkCETmTr_kHqkcqqBFw@mail.gmail.com>
 <20190926141814.GA24606@octa>
Message-ID: <CAFJf9KPvYdNgK0bBd2UKbBkDHjdkbusk9oGN+t=JkatCtmzhgA@mail.gmail.com>

On Thu, Sep 26, 2019 at 3:18 PM Daniel Trstenjak <daniel.trstenjak at gmail.com>
wrote:

> Hi John,
>
> 'ghc' won't automatically use the packages you've installed with 'cabal
> install',
> but you've to add them to the 'ghc' call.
>

Thanks, that'll be the key to what's going on.  I had assumed that
installed packages would be automatically available for "import", as they
are in Python.  (The program I'm writing has the same functionality as a
Python program I had written earlier, which probably biased me to thinking
that way.)

__John
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