I'm a newbie, knowing a little about Haskell, and hope my question isn't very silly... ===================================================================== My absolute value function looks like this: abs2 :: Num a => a -> a abs2 n = if n >= 0 then n else 0 - n GHCi tells me that I should add Ord type class to its definition. Well, it's true. It has used relational operators and Num isn't a subclass of Ord. However, when I input ":t abs" in GHCi, the interpreter shows "abs :: Num a => a -> a". I read GHC/Num.lhs and find that abs is defined as "abs :: a -> a" and has no concrete content. So I think the abs function is written in C as a module to implement directly and the type of abs just follows its class GHC.Num. Is it right? Or there are any other reasons? Thanks, Hengruo