[Haskell-cafe] "Could not find module ... which is hidden" problem

[Alexander Dunlap]

On Sat, Nov 29, 2008 at 11:22 PM, Belka <lambda-belka at yandex.ru> wrote:
>
> Hello!
>
> ----------------------------START----------------------------------
> $ sudo runghc Setup configure --user
> Configuring HCL-1.2...
>
> $ sudo runghc Setup build
> Preprocessing library HCL-1.2...
> Preprocessing executables for HCL-1.2...
> Building HCL-1.2...
>
> HCL.hs:302:7:
>    Could not find module `System.Random':
>      it is a member of package random-1.0.0.1, which is hidden
>
> $ sudo ghc-pkg expose random
> Saving old package config file... done.
> Writing new package config file... done.
>
> $ sudo runghc Setup configure --user
> Configuring HCL-1.2...
>
> $ sudo runghc Setup build
> Preprocessing library HCL-1.2...
> Preprocessing executables for HCL-1.2...
> Building HCL-1.2...
>
> HCL.hs:302:7:
>    Could not find module `System.Random':
>      it is a member of package random-1.0.0.1, which is hidden
>
> ---------------------THE-END----------------------------------------
>
> Perhaps, i'm 1000th, who asks how to solve this. Sorry that didn't search
> better, but it's really tiring for a newby. :-(
> [ http://www.haskell.org/haskellwiki/Upgrading_packages/Updating_to_GHC_6.8
> Here ] found something, which maybe called "a gentle explaination" of what's
> going on. I have ghc ver: 6.8.2, base ver: 3.0.1.0.
>
> So there are 2 questions of mine:
> (1) Is there any centralized and well organized Haskell Knowledge Base,
> where it would be much easier to find solutions for "popular" problems?
> Anybody, please, your recommendations.
> (2) As for the topic: the only option for me would be obtaining older GHC
> (base?) - is that correct? So that require me reinstalling every Haskell
> package I have installed so far?
>
> Thanks in advance.
> --
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>
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Is the "random" package in the build-depends of your cabal file? If
not, that's why it's hidden. Cabal hides all of the packages that
aren't  listed in build-depends so that you can't accidentally depend
on something that you don't list.

Hope that helps.

Alex