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September 2019

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2 discussions

Import errors from a very simple program
by John Sturdy 27 Sep '19

27 Sep '19

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/NamedBasedGener… (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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Re: [Haskell-beginners] how to convert an array of foreignPtr a into a list of Ptr a
by 鲍凯文 03 Sep '19

03 Sep '19

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(a)haskell.org> wrote: > Send Beginners mailing list submissions to > beginners(a)haskell.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners > or, via email, send a message with subject or body 'help' to > beginners-request(a)haskell.org > > You can reach the person managing the list at > beginners-owner(a)haskell.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Beginners digest..." > > > Today's Topics: > > 1. how to convert an array of foreignPtr a into a list of Ptr a > (PICCA Frederic-Emmanuel) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Tue, 27 Aug 2019 07:19:25 +0000 > From: PICCA Frederic-Emmanuel > <frederic-emmanuel.picca(a)synchrotron-soleil.fr> > To: "The Haskell-Beginners Mailing List - Discussion of primarily > beginner-level topics related to Haskell" <beginners(a)haskell.org> > Subject: [Haskell-beginners] how to convert an array of foreignPtr a > into a list of Ptr a > Message-ID: > < > A2A20EC3B8560D408356CAC2FC148E53016CF535AB(a)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 > > ------------------------------ > > Subject: Digest Footer > > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners > > > ------------------------------ > > End of Beginners Digest, Vol 134, Issue 4 > ***************************************** >

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