Re: [Haskell-cafe] Example code won't compile

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