Perfectly valid question. This explains the practice in incremental dev or refactoring of using "undefined" in stub/placeholder functions to get the type signatures but not function bodies in:

http://www.fatvat.co.uk/2009/09/generating-text-in-haskell.h...

Also: 2 longish threads about this

http://www.reddit.com/r/programming/duplicates/tjeg3/haskell...