[Haskell-cafe] a Char->Char function?

Hello, I am writing a function(actually much more than this): bozo :: Char -> Char bozo 0x02 = 'a' ... However, I get complaints from ghc suggesting that I should add an "instance declaration (Num, Char). I (mistaking) thought I understood the Haskell class hierarchy and the associated constraints .. but apparently not .. => help please. Should Kind regards, Vasya