From: Krzysztof Skrzętnicki <gtener@gmail.com>
Subject: Re: [Haskell-cafe] Example code won't compile
To: "michael rice" <nowgate@yahoo.com>
Cc: "Lennart Augustsson" <lennart.augustsson@gmail.com>, "haskell-cafe@haskell.org" <haskell-cafe@haskell.org>
Date: Friday, May 15, 2009, 9:55 PM

The one important line is
> import Control.Monad.Error
It adds dependancy on mtl package, which is not used by default
(contrary to 'base' package, which includes Monad, System and IO
modules). With --make GHC adds it automatically. Therefore
$ ghc -package mtl ex14.hs
compiles fine. I'd recommend using --make. In rare occasions when
there is a namespace clash between packages one can simply hide
offending packages or specify preferred ones.

Best regards

Christopher Skrzętnicki