I am currently self studying Haskell. I am just a beginner so I haven't yet had a need to use cabal or stack. But right now I need to test some of my code using QuickCheck.
From this link that I found https://github.com/haskell/cabal/blob/master/doc/cabal-commands.rst , I ran the command cabal install --lib QuickCheck --package-env . and got the following output :
axiom#pop-os:~/Desktop/Haskell-Learning/Course/Homework 10$ cabal install --lib QuickCheck --package-env .
Resolving dependencies...
Up to date
In the same directory, I have a .hs file and in that when I tried to import Test.QuickCheck the linter gives an error as the package doesnt seem to be available for importing.
Then I ran cabal repl --build-depends QuickCheck and then in ghci I was able to import it. But still it was not importing in the code file.
Then when I just opened ghci by firing the command ghci , the following shows up, which suggests that there is a package environment here in this directory :
GHCi, version 8.10.7: [https://www.haskell.org/ghc/](https://www.haskell.org/ghc/) :? for help
Loaded package environment from /home/axiom/Desktop/Haskell-Learning/Course/Homework 10/.ghc.environment.x86\_64-linux-8.10.7
Prelude> import Test.QuickCheck
Prelude Test.QuickCheck> :q
Even after above, that is, being able to import QuickCheck in GHCi, the import is still not working in the file.
After this, I tried the following :
axiom#pop-os:~/Desktop/Haskell-Learning/Course/Homework 10$ cabal install QuickCheck
Resolving dependencies...
Up to date
Warning:
############################################################
# WARNING: Installation might not be completed as desired! #
############################################################
The command "cabal install [TARGETS]" doesn't expose libraries.
* You might have wanted to add them as dependencies to your package. In this
case add "QuickCheck" to the build-depends field(s) of your package's .cabal
file.
* You might have wanted to add them to a GHC environment. In this case use
"cabal install --lib QuickCheck". The "--lib" flag is provisional: see
https://github.com/haskell/cabal/issues/6481 for more information.
axiom#pop-os:~/Desktop/Haskell-Learning/Course/Homework 10$ cabal install --lib QuickCheck
Resolving dependencies...
Up to date
The import still doesn't work.
Any help is appreciated !
The method I ended up finding is the following :
Run the following in the directory where you have your haskell file where you want to import an external package :
cabal init
This will general a small number of files and such in that directory.
Add the name of the package that you want to use in the .cabal file that was generated . For example, I wanted to use QuickCheck so my .cabal file looks like this :
cabal-version: 2.4
name: Homework10
version: 0.1.0.0
author: Name Surname
maintainer: name#email.com
extra-source-files: CHANGELOG.md
executable Homework10
main-is: Main.hs
build-depends: base ^>=4.14.3.0, QuickCheck
hs-source-dirs: app
default-language: Haskell2010
Then in the same directory, run the following :
cabal build
Then when you try to import the package in your .hs, you should be able to do so.
Related
I am new to Haskell. I want to use Control.Lens package. I've read this and applied what it says but I get an error that says:
Resolving dependencies...
cabal-3.6.2.0.exe: Cannot build the executables in the package lens because it
does not contain any executables. Check the .cabal file for the package and
make sure that it properly declares the components that you expect.
when I try to run cabal install lens in the project folder.(I opened terminal in the project folder.)
Any help would be appreciated.
Solution: I've learned that I need to add 'lens' into build-depends part of .cabal file.Then I need to import Control.Lens inside Main.hs . I give my .cabal file as an example:
executable Prelude3
main-is: Main.hs
-- Modules included in this executable, other than Main.
--other-modules: Basic
-- LANGUAGE extensions used by modules in this package.
-- other-extensions:
build-depends: containers,lens,microlens,microlens-platform,base ^>=4.14.3.0
hs-source-dirs: app
default-language: Haskell2010
On the top of the Main.hs I write import Control.Lens. Finally after I run 'cabal build' and cabal run in the terminal necessary packages successfully downlaoaded.
I put this in a file (see bottom) and got the following error when loading it in ghci (i.e. start ghci then :l file):
7:13: error:
• Couldn't match expected type ‘network-uri-2.6.1.0#network-uri-2.6.1.0-7BN1tbB3iHQ2XgvmqLAYph:Network.URI.URI’
with actual type ‘Network.URI.URI’
NB: ‘Network.URI.URI’
is defined in ‘Network.URI’
in package ‘network-uri-2.6.1.0#network-uri-2.6.1.0-80FpvaNUTSDFCPv0sSze40’
‘network-uri-2.6.1.0#network-uri-2.6.1.0-7BN1tbB3iHQ2XgvmqLAYph:Network.URI.URI’
is defined in ‘Network.URI’
in package ‘network-uri-2.6.1.0#network-uri-2.6.1.0-7BN1tbB3iHQ2XgvmqLAYph’
Have I somehow installed two slightly different versions of network-uri, or what is this? How do I resolve it?
I've hardly used cabal but tried cabal install --reinstall network-uri, went fine but problem persists.
File contents:
import Network.HTTP
import Network.URI (parseURI)
import Data.Maybe (fromJust)
myRequestURL = "http://www.virginia.edu/cgi-local/ldapweb"
myRequest :: String -> Request_String
myRequest query = Request {
rqURI = fromJust $ parseURI myRequestURL
, rqMethod = POST
, rqHeaders = [ mkHeader HdrContentType "text/html"
, mkHeader HdrContentLength $ show $ length body ]
, rqBody = body
}
where body = "whitepages=" ++ query
main :: IO ()
main = do
response <- simpleHTTP $ myRequest "poon"
putStrLn ""
EDIT Re-installed haskell-platform. After this, ghc-pkg list reports all packages to be under (?) /usr/lib/ghc/package.conf.d, and the program I tried to copy loads just fine.
EDIT 2 After running cabal install some-pkg, ghc-pkg list reports that the newly installed stuff is in another directory. Indeed, ~/.cabal/config specifies install dirs for user, as well as install dirs for global. How is all this supposed to be managed properly?
GHC understands the concept of package databases. Cabal manages multiple package databases. There's a system package database, and a user package database. When you compile something with Cabal V1, it uses the union of these package databases. This is a bit of a time bomb, because, as you see, GHC does not like it when you have multiple of the same package. When you issued cabal install network-uri, cabal decided to install one copy of that package into your user database, though you already had one in the system database. When you tried to use ghc, it picked up on the two copies and got confused. Because cabal does not support removing packages, your Haskell installation was pretty much borked, and you reinstalled. I believe you could have done a more conservative rm ~/.ghc, or, had you been really adventurous, used the low-level ghc-pkg command to edit the package database.
Now that you've reinstalled the Platform, I would heavily recommend never using cabal install again. It's old, it's broken, cabal itself tells you not to use it. If you're using the Platform, I think it has stack in it, which is a different build manager, based on Cabal, which is not prone to this kind of breakage. Or, you can just stick to the V2 series of cabal commands, which is what I prefer.
Cabal V2 does not directly support your usecase, where you install a package globally and compile a program against it. This is because doing so is fundamentally broken: global package databases really just don't work for GHC. What Cabal V2 does is install packages into your home directory, ~/.cabal/store. You then have to explicitly tell it which packages you want, and it will construct a package database that contains each required package, without any wonkiness. You can get a REPL with a certain set of packages by issuing (this will take you to a temporary directory; you may need to :cd yourself back.)
cabal v2-repl -b network-uri -b package2 -b etc
If you want to actually compile files with ghc with a set packages, you have to actually define a package with a .cabal file. Here's a stub .cabal file:
name: temporary-pkg
version: 0.0.0.0
build-type: Simple
cabal-version: >=2.0
executable main -- if there is no Main, say "library" instead of "executable <name>"
default-language: Haskell2010
main-is: Main.hs -- only valid in executable stanzas
hs-source-dirs: src -- source files go here
build-depends: base, network-uri, package2, etc -- packages go here
Create and enter a directory, place that in temporary-pkg.cabal, place your sources in src/, and you can issue stuff like cabal v2-build and cabal v2-repl and cabal v2-exec main, etc. cabal will go off and install dependencies from Hackage into ~/.cabal/store as needed. cabal v2-install is therefore not that useful here. In general, v2-installing libraries is unnecessary, but v2-installing packages with executables is useful. Again, for hygiene reasons, you have to list all the packages you are importing from, but you don't need to list their dependencies or anything insane like that.
Cabal V2 still doesn't support uninstalling packages, though the point is that should not be necessary. However, if you find ~/.cabal/store getting too large for your liking, you can just nuke it, and should be built back up as packages are requested.
I am working on the "roman-numerals" task from the exercism Haskell track and followed their instructions to installing stack. I am working on a Fedora 24 box.
As long as I was working with Haskell modules from base, I didn't have a problem. Now I am trying to import the Data.Map module. It works fine using the ghci command line:
$ ghci
GHCi, version 7.8.4: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> import Data.Map
Prelude Data.Map>
However, when I try to import it from inside my src file with the command:
import qualified Data.Map as M (foldlWithKey, fromList)
I am running into problems when I try to run the test:
$ stack test
roman-numerals-0.0.0: build (lib + test)
Preprocessing library roman-numerals-0.0.0...
[2 of 2] Compiling Roman (...)
(...) /roman-numerals/src/Roman.hs:3:1: error:
Failed to load interface for ‘Data.Map’
It is a member of the hidden package ‘containers-0.5.7.1’.
Perhaps you need to add ‘containers’ to the build-depends in your .cabal file.
Use -v to see a list of the files searched for.
Progress: 1/2
(...)
I googled the problem and found a straightforward solution at the Cabal FAQ at haskell.org:
What you need to do is to add containers to the build-depends in your .cabal file.
I am assuming they mean the file roman-numerals.cabal that is in my working directory. The contents are:
-- This file has been generated from package.yaml by hpack version 0.14.0.
--
-- see: https://github.com/sol/hpack
name: roman-numerals
version: 0.0.0
build-type: Simple
cabal-version: >= 1.10
library
hs-source-dirs:
src
build-depends:
base
exposed-modules:
Roman
other-modules:
Paths_roman_numerals
default-language: Haskell2010
test-suite test
type: exitcode-stdio-1.0
main-is: Tests.hs
hs-source-dirs:
test
build-depends:
base
, roman-numerals
, hspec
default-language: Haskell2010
I tried to add "containers" to the build-depends in either and both the "library" and "test-suite" sections, but when I run
$ stack test
the error persists, and the .cabal file is reverted to the same contents shown above.
Any pointers? Much appreciated!
This is hinting at the problem:
-- This file has been generated from package.yaml by hpack version 0.14.0.
--
-- see: https://github.com/sol/hpack
hpack is an alternative, YAML-based specification format for Haskell packages which can be used instead of the traditional cabal format. The hpack program can then be used to convert a specification from the hpack format to the cabal format to be able to integrate with the rest of the Haskell toolchain.
Some basic support for hpack was added to stack some time ago. It checks for a file called package.yaml in the current directory, which is the standard name for hpack format package specifications, and if it exists, it runs hpack to convert it to a cabal file and then proceeds building as normal. This is what's trampling over your .cabal file.
To solve this, either:
Modify package.yaml instead of roman-numerals.cabal to achieve the same effect.
Delete package.yaml and continue working directly with roman-numerals.cabal.
The syntax for adding dependencies in the hpack format is:
dependencies:
- base
- containers
I installed diagrams, and it seems to be there, but GHCi doesn’t find it. I tried adding the local sandbox to the command line (-package-db), but still no luck.
Any suggestions?
C:\Users\guthrie>
C:\Users\guthrie>cabal install diagrams
Resolving dependencies...
All the requested packages are already installed:
diagrams-1.2
Use --reinstall if you want to reinstall anyway.
I find it in:
C:\Users\guthrie\.cabal-sandbox\i386-windows-ghc-7.6.3-packages.conf.d
(diagrams-1.2, diagrams-contrib, -core, -lib, -svg)
But running: “cabal repl” or using the GHC(i) flag “-package-db=…”
fail to find it:
C:\Users\guthrie>cabal repl
GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> :m + Diagrams.Prelude
<no location info>:
Could not find module `Diagrams.Prelude'
It is not a module in the current program, or in any known package.
Prelude>
To clarify; ignoring the cabal invocations, using GHC/i directly, and the program diagramsDemo.hs:
-- http://projects.haskell.org/diagrams/doc/quickstart.html
--
import Diagrams.Prelude
import Diagrams.Backend.SVG.CmdLine
main = mainWith (circle 1 :: Diagram B R2)
Gives:
C:\Users\guthrie\Desktop\xFer\Graphics>ghc --make diagramsDemo.hs
diagramsDemo.hs:7:8:
Could not find module `Diagrams.Backend.SVG.CmdLine'
Use -v to see a list of the files searched for.
C:\Users\guthrie\Desktop\xFer\Graphics>ghc --make diagramsDemo.hs -package-db=C:\Users\guthrie\.cabal-sandbox\i386-windows-ghc-7.6.3-packages.conf.d
diagramsDemo.hs:7:8:
Could not find module `Diagrams.Backend.SVG.CmdLine'
Use -v to see a list of the files searched for.
As bheklilr said, if ghci is started with cabal repl, it will only find packages specified as a dependency in the .cabal file.
However you can start it with cabal exec ghci, then it will find all packages installed in the sandbox.
The same is true for invoking ghc (cabal build vs. cabal exec ghc), but note that if you want to pass flags you have to use --, like in cabal exec ghc -- -O2 Main.hs. Alternatively you can use cabal exec bash and launch ghci or ghc in the new shell.
cabal exec was added with Cabal 1.20.
Today I installed windows 8.1 and haskell on my laptop. I'm trying to build my own haskell library, but I got an error when I try to use cabal sdist. This is the error:
D:\Development\School\AFP\Assignments\Practice\Exercise\Project>cabal sdist
Distribution quality errors:
'license: NONE' is not a recognised license. The known licenses are: GPL,
GPL-2, GPL-3, LGPL, LGPL-2.1, LGPL-3, AGPL, AGPL-3, BSD2, BSD3, MIT, ISC,
MPL-2.0, Apache, Apache-2.0, PublicDomain, AllRightsReserved, OtherLicense
Distribution quality warnings:
No 'category' field.
No 'maintainer' field.
No 'synopsis' field.
A 'license-file' is not specified.
When distributing packages it is encouraged to specify source control
information in the .cabal file using one or more 'source-repository' sections.
See the Cabal user guide for details.
Note: the public hackage server would reject this package.
Warning: Cannot run preprocessors. Run 'configure' command first.
Building source dist for Project-0.1.0.0...
cabal: does not exist
Before I used the "cabal sdist" I used the following commands:
cabal init
cabal sandbox init
cabal install -j
Every command succeed, except for the cabal sdist. The cabal install only gives the following warning:
D:\Development\School\AFP\Assignments\Practice\Exercise\Project>cabal install -j
Resolving dependencies...
In order, the following will be installed:
Project-0.1.0.0 (reinstall)
Warning: Note that reinstalls are always dangerous. Continuing anyway...
Notice: installing into a sandbox located at
D:\Development\School\AFP\Assignments\Practice\Exercise\Project\.cabal-sandbox
Configuring Project-0.1.0.0...
Building Project-0.1.0.0...
Installed Project-0.1.0.0
This is my Project.cabal file:
-- Initial Project.cabal generated by cabal init. For further
-- documentation, see http://haskell.org/cabal/users-guide/
-- Initial Project.cabal generated by cabal init. For further
-- documentation, see http://haskell.org/cabal/users-guide/
name: Project
version: 0.1.0.0
-- synopsis:
description: Education
license: NONE
-- license-file:
-- author:
-- maintainer:
-- copyright:
-- category:
build-type: Simple
extra-source-files: File6, File5, File4, File3, File2
cabal-version: >=1.10
library
exposed-modules: File1
-- other-modules:
-- other-extensions:
build-depends: base >=4.8 && <4.9, QuickCheck >=2.8 && <2.9
hs-source-dirs: src
default-language: Haskell2010
I tried google, but I can't find a good solution. I use the following versions:
Cabal version: 1.22.4.0
Haskell version: 7.10.2
If you need more information, please ask.
I don't know anything about sdist, but the problem is clear: you've specified 'NONE' as the license in your cabal file, but that is not allowed for the sdist option. configure, build, and init don't care about the specific license, but sdist apparently does.
For more info, I searched google for "cabal sdist" and found this.
This [cabal sdist] has the advantage that Cabal will do a bit more checking, and ensure that the tarball has the structure that HackageDB expects.
HackageDB probably expects a valid license, hence why "NONE" is not allowed.
The problem was that cabal could not find the files in extra-source-files. I thought I didn't had to add the extension of the haskell files, but this is required.
I also had another problem. The extra-source-files wasn't using the hs-source-dirs, so I had to explicitly write "src/" infront of a file.