missing mtl (which exists) when installing filemanip package

[HP Wei]

I did the following:
   download filemanip-0.3.6.2.tar.gz
   tar xvf ...
   cd filemanip-0.3.6.2
   runhaskell Setup configure --prefix=$HOME/ghc

   --> it tells me
       Setup: At least the following dependencies are missing:
       mtl -any, unix-compat -any

So, I did the following:
    download unix-compat-0.4.1.0.tar.gz
    tar xvf ...
    cd unix-compat-0.4.1.0
    runhaskell Setup configure --prefix=$HOME/ghc
    runhaskell Setup build
    runhaskell Setup install

   --> under $HOME/ghc/lib
       I see unix-compat-0.4.1.0/ that was newly added by the Setup
       processes.

   --> under $HOME/ghc/lib
       I also see mtl-2.0.1.0/
       This was there already before the above operations.

Then, I went back
    cd filemanip-0.3.6.2
    runhaskell Setup configure --prefix=$HOME/ghc

    --> it tells me
        Setup: At least the following dependencies are missing:
        mtl -any

Question:
    why can't $HOME/ghc/lib/mtl-2.0.1.0/
    be recognized during the above Setup configure ??

    What do I need to do ?

thanks
HP