Haskell Could not find module `System'

Question

I'm new with Haskell and have trouble with its package.

I want to import System.Random but

Could not find module `System.Random'

Then I tried to import System but

Could not find module `System'.

It is a member of the hidden package `haskell98-2.0.0.0'.

I tried to search this problem, but those solutions still don't work.

As this said, I tried to install cabal on my Mac OS X using MacPort, but

Error: The following dependencies were not installed: ghc Error: Status 1 encountered during processing.

I have installed Haskell Platform and can use ghci in command-line. GHCi, version 7.2.1

Then I tried to use ghc-pkg expose haskell98-2.0.0.0 as this one says.

But this time, I can't even run ghci.

Top level:

Ambiguous interface for `Prelude':

it was found in multiple packages: base haskell98-2.0.0.0

So, what can I do without using cabal?

The Haskell Platform should come with Cabal. You shouldn't need to install anything else (other than the random package -- `cabal install random`) — Tyler, Sep 01 '11 at 16:40
According to the page you linked, Haskell Platform based on GHC 7.2.x has not been released yet. You are asking for troubles if you have replaced GHC in Haskell Platform. — Tsuyoshi Ito, Sep 02 '11 at 21:05

score 23 · Accepted Answer · answered Sep 01 '11 at 02:39

23

The System.Random module belongs to the random package, which is no longer included with GHC as of version 7.2.1.

I'm not sure what to do about your Cabal problem, as I'm not familiar with Mac OS X, but I'd recommend getting that to work first. Installing random should then be trivial using Cabal.

As a possible workaround, you might want to consider using an older version of GHC.

answered Sep 01 '11 at 02:39

hammar

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but the `Random` module still exists – user102008 Sep 01 '11 at 03:37
@user102008 Then how can I use it? `import Random` also doesn't work. – Ovilia Sep 01 '11 at 03:41
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@Ovilia: `Random` belongs to the `haskell98` package, but [this package can no longer be used together with `base` as of GHC 7.2.1](http://www.haskell.org/ghc/docs/7.2.1/html/users_guide/release-7-2-1.html#id569061). – hammar Sep 01 '11 at 03:43
@hammar It finally worked when I use an old version of GHC, thx. – Ovilia Sep 01 '11 at 15:46
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@Olivia don't resort to old version of GHC, just don't use haskell98 – alternative Sep 01 '11 at 23:06

score 18 · Answer 2 · answered Feb 13 '12 at 07:26

18

the cabal incantation:

cabal install random

answered Feb 13 '12 at 07:26

ssanj

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won't this be a global install and should be discouraged? instead the dependencies should be added to the .cabal file? – dade Aug 10 '20 at 12:10
yeah, you're right. You could use a cabal sandbox these days. – ssanj Aug 12 '20 at 01:44

score 0 · Answer 3 · answered Aug 12 '20 at 03:20

The answer here is a little bit dated and would lead to a global install and should be discouraged.

A better approach will be to add the random package as dependency in the .cabal file.

Something like this:

build-depends:       base ^>=4.13.0.0 --base package
                   , random           -- random package where System.Random can be found

score 0 · Answer 4 · answered Jul 20 '22 at 19:54

cabal repl -b random # -b is short for --build-depends

This answer was based on another stackoverflow thread here. Basically it installs the package random as a dependency of your project rather than installing it globally. Packages are installed globally if you just write cabal install random - which we dont usally want.

Haskell Could not find module `System'

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