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Today's Topics:
1. Import errors from a very simple program (John Sturdy)
2. Re: Import errors from a very simple program (Francesco Ariis)
3. Re: Import errors from a very simple program (Daniel Trstenjak)
4. Re: Import errors from a very simple program (John Sturdy)
----------------------------------------------------------------------
Message: 1
Date: Thu, 26 Sep 2019 14:53:23 +0100
From: John Sturdy <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] Import errors from a very simple program
Message-ID:
<cafjf9knhvy5qpyyhm0xtnokqzozeoshfkcetmtr_khqkcqq...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
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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Message: 2
Date: Thu, 26 Sep 2019 16:15:40 +0200
From: Francesco Ariis <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Import errors from a very simple
program
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
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
------------------------------
Message: 3
Date: Thu, 26 Sep 2019 16:18:14 +0200
From: Daniel Trstenjak <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Import errors from a very simple
program
Message-ID: <20190926141814.GA24606@octa>
Content-Type: text/plain; charset=us-ascii
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
------------------------------
Message: 4
Date: Thu, 26 Sep 2019 15:26:22 +0100
From: John Sturdy <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] Import errors from a very simple
program
Message-ID:
<CAFJf9KPvYdNgK0bBd2UKbBkDHjdkbusk9oGN+t=jkatctmz...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
On Thu, Sep 26, 2019 at 3:18 PM Daniel Trstenjak <[email protected]>
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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