The Haskell Platform is a comprehensive, robust development for programming
in Haskell, which not only makes it trivial to get up and running with a full
Haskell development environment, but also provides a comprehensive, standard
base for commercial and open source Haskell development that maximises
interoperability and stability of your code.

This requires ghc, and hscolour is an optional requirement.

This is intended to be installed on a system that does not already have any
haskell-related components (other than ghc & hscolour, of course) installed,
so for best results (and chance of success), you should remove any of those
before you try to build haskell-platform.