CODEWITHSUNDEEP
haskellcabalhaskell-stack
domoremath
domoremath

Reputation: 555

How to install system.random. Maybe cabal issue in version 8 of stack

I am working on Ubuntu 16.04 with stack ghci version 8. I want to import System.Random in Haskell but it seems I am having trouble that may involve Cabal. I have seen similar posts on this website but they usually say it is because of an older version but I am using version 8.

I get the error:

Failed to load interface for ‘System.Random’
Use -v to see a list of the files searched for.

which tells me I have problems with System.Random. Looking online, I found that I need to first install Cabal.

When I type 

Cabal --version

I get 

cabal-install version 1.22.6.0
using version 1.22.5.0 of the Cabal library

which tells me I already have it. So when I try to update with

sudo apt-get install cabal-install cabal update

I get

Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package cabal
E: Unable to locate package update

which is weird. If I ignore it and try to install random anyways through

cabal install random

I get

Resolving dependencies...
All the requested packages are already installed:
random-1.1
Use --reinstall if you want to reinstall anyway.

So it seems I also have the random package of cabal. But I can't load a program with the 

import System.Random

command.

EDIT: It seems I have stack ghci version 8.0.1 and ghci version 7.10.3. The System.random loads in ghci but not stack ghci.

I also get the following when I try to load a file in stack. Entering

stack ghci R.hs

I get

Warning: Couldn't find a component for file target /home/aa/workspace/share/haskell/chenw/hw4/R.hs. Attempting to load anyway.
Configuring GHCi with the following packages: 
GHCi, version 8.0.1: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/aa/.ghc/ghci.conf
Loaded GHCi configuration from /tmp/ghci19674/ghci-script

Does this mean there is something wrong with my install of stack?

Upvotes: 3

Views: 16353

Answers (1)

wizzup
wizzup

Reputation: 2411

If you want to use stack, and assume you have a working stack, you don't have to install anything via apt-get.

First, update your stack

stack update

Make sure you having the right resolver version number for your packages

  • If you want to use stack globally ,i.e., stack ghci <source.hs>. Check ~/.stack/global-project/stack.yaml.
  • If you manage your project using stack, i.e,. stack new <project>, stack build. Check project's stack.yaml

To use stack globally (anywhere)

  • install random by stack install random
  • using GHCi by stack ghci and :load <source.hs>
  • compile source by stack ghc <source.hs>
  • run your program by stack exec <executable_name>

You can force stack to use specific resolver by using --resolver=.

Example: using latest lts 

$ stack --resolver=lts setup
$ stack --resolver=lts install random
$ stack --resolver=lts ghci

To use stack in a project directory (stack.yaml exists), you don't need to install package manually; stack will install it for you, if needed, when stack build. But you have to edit <project.cabal>

build-depends:       base >= 4.7 && < 5
                     , random

Upvotes: 6

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