Hi! I have a few questions to improve my knowledge of Haskell. I didn't stumble over these problems while working on specific tasks, I more or less constructed them explicitly to get an adequate understanding of the basic Haskell semantics. 1 Why can't I apply a class directly to all instances of another, existing class? For example why is it possible to write class Test a instance Num a => Test [a] but not with instance Num a => Test a in the last row? 2 Why is the following example not valid? f :: a -> a f '0' = 0 f x = 1 I think the reason lies in the type system but I can't locate it exactly. 3 Why is the following legal [] :: Num a => [a] but not with a self declared class instad of Num (unresolved overloading)? 4 Why does in the declaration f undefined = '0' the expression undefined work apparently in the same way as a wildcard? Thanks, fweth