[Haskell-cafe] How do I fix this error message?

Peter Verswyvelen bugfact at gmail.com
Fri Sep 4 17:07:40 EDT 2009

Although also a bit of a global hack, you could also hide one of  the
packages using

ghc-pkg hide mtl-1.1.02

instead of uninstalling them I think.

Also, if you make a cabal file, you could specify the exact module you
want to use.

On Fri, Sep 4, 2009 at 11:03 PM, Michael Vanier<mvanier42 at gmail.com> wrote:
> Hi everyone,
> I ran into this error when recompiling some code I hadn't worked on in a
> while:
> Foo.hs:19:7:
>   Could not find module `Control.Monad.Error':
>     it was found in multiple packages: monads-fd- mtl-
> I gather that monads-fd is supposed to be a replacement for mtl, but I have
> both of them (mtl from the normal GHC 6.10.4 install, monads-fd from cabal).
>  I don't really care which one I use, though mtl has been fine in the past.
>  In the past, I had to manually uninstall cabal packages that used
> incompatible libraries.  Is this still the case?
> TIA,
> Mike
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