Haskell Could not find module `System'

The System.Random module belongs to the random package, which is no longer included with GHC as of version 7.2.1.

I'm not sure what to do about your Cabal problem, as I'm not familiar with Mac OS X, but I'd recommend getting that to work first. Installing random should then be trivial using Cabal.

As a possible workaround, you might want to consider using an older version of GHC.

the cabal incantation:

cabal install random