Undefined Title

could not find module Control.Monad.Writer


I use GHCi version 7.4.2 on MacOSX 10.8.2 and also Haskell Platform. Then, I ran into a next error about importing module.

Prelude> :m Control.Monad.Writer
<no location info>:
  Could not find module `Control.Monad.Writer'
  Perhaps you meant
    Control.Monad.Fix (from base)
    Control.Monad.Zip (from base)
Prelude> :m Control.Monad.
Control.Monad.Fix        Control.Monad.ST       Control.Monad.ST.Lazy.Safe    Control.Monad.ST.Safe    Control.Monad.ST.Unsafe
Control.Monad.Instances  Control.Monad.ST.Lazy  Control.Monad.ST.Lazy.Unsafe  Control.Monad.ST.Strict  Control.Monad.Zip

At first, I couldn’t find Control.Monad.Writer. But now, I can find it though I’m not sure why it is found.

I remember I tried ghc-pkg list, ghc-pkg dump and ghc-pkg recache. I’ve never tried any special things…

Mh… have to be familier with Haskell GHC environment.