I have done this and it has only removed GHC, not the rest of the Haskell Platform.

On Tue, Mar 15, 2011 at 1:40 AM, Daniƫl de Kok <me@danieldk.eu> wrote:
On Monday, March 14, 2011 at 3:22 PM, Jesse Schalken wrote:
Simple question which an hour of googling and a question on #haskell couldn't satisfy. :(
>
> I have installed the Haskell Platform 2011.2.0.0 on Mac OS X 10.6.6.
> Now how do I uninstall it?

sudo /Library/Frameworks/GHC.framework/Versions/Current/Tools/Uninstaller