[Haskell-cafe] Nice clean code example?

I'd like to showoff some nice Haskell code to a CTO with no experience with FP. I promised to send him a small piece of Haskell so he could get an idea. The code should be easy to read, without obscure looking operators (so sorry, no lens, arrows stuff like that), optionally even do something interesting. Who has the nicest example laying around? (and yes, I need it by yesterday ;-) ) Thanks!