Haskell Hacking

I found the first of a set of Haskell introductions just before Christmas but have only now got around to giving it a go.  Here's a link to the first one:
http://cgi.cse.unsw.edu.au/~dons/blog/2006/12/16#programming-haskell-intro

I had a few problems installing ghc on the Mac OS X side so I installed Ubuntu (Edgy) in a Q (qemu) virtual machine and after learning about enabling the 'universe' respository in sources.list installed 'ghc6' and 'haskell-mode' (the emacs editing mode for haskell). 

I read all three articles and have started hacking with number three - the 'cat' clone.  Things are going reasonably at the moment except ghc doesn't like the 'set' in concatMap.  I don't have a clue at the moment what might be wrong, but I suppose that comes from learning new stuff...