[Haskell-cafe] Strange Type Error

[Christopher Done]

The problem is the monomorphism restriction:

http://www.haskell.org/haskellwiki/Monomorphism_restriction
http://www.haskell.org/ghc/docs/7.0.2/html/users_guide/monomorphism.html
http://stackoverflow.com/questions/tagged/monomorphism-restriction
http://www.cs.auckland.ac.nz/references/haskell/haskell-intro-html/pitfalls.html

This kicks everyone in the butt at least once. It would be good if GHC
could point it out, as mine (6.12.3) just complains about no instance.
Maybe GHC7 does point it out. It's a waste of people's time otherwise.