[Haskell-beginners] Disappearing Module Problem

[Antoine Latter]

On Mon, Sep 12, 2011 at 3:54 PM, Michael Craig <mkscrg at gmail.com> wrote:
> I was using "cabal install aeson" and "cabal install http-enumerator".
> Running the combined command fixed the issue. I'd forgotten that cabal
> allows for it.
> Is this necessary because of mutual dependencies? With the Platform
> installation of cabal, I could run cabal install for each package and
> everything would work fine. What's the difference?
>

What happens is that when you run "cabal install" with multiple
arguments, the dependency resolver tries to come up with an install
plan that jointly satisfies the dependencies of all arguments.

When you do the installs one at a time it is possible in some cases to
break already installed packages. One way to check for this is to use
the 'ghc-pks' command to look for broken packages.

Antoine

> Best,
> Mike S Craig
> (908) 328 8030
>
>
> On Mon, Sep 12, 2011 at 4:46 PM, Antoine Latter <aslatter at gmail.com> wrote:
>>
>> On Mon, Sep 12, 2011 at 3:34 PM, Michael Craig <mkscrg at gmail.com> wrote:
>> > I'm trying to install aeson and http-enumerator on an otherwise fresh
>> > installation of ghc 7.2 on OS X 10.7. I was inspired by beastaugh's gist
>> > on
>> > getting cabal-install running on Lion: https://gist.github.com/1169332.
>> > I can install either aeson or http-enumerator and it'll work fine.
>> > However,
>> > as soon as I install the second one the first one disappears. The files
>> > are
>> > all there in .cabal/lib, but ghc can't find the module.
>> > Any ideas?
>> >
>>
>> What command are you using to install these, specifically?
>>
>> What does the following do:
>>
>> > cabal install aeson http-enumerator
>>
>> Thanks,
>> Antoine
>>
>> > Mike S Craig
>> >
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>> >
>> >
>
>