Hi A function inc5 inc5 :: Float -> Float inc5 x = x + 5 can only be a member of a type class A, if we make all functions from Float -> Float members of type class A. Thus, I assume, that _type_ class is named type class, as membership is decided by types. However, it makes no sense to say that all functions from Float -> Float are invertible or continuous. We would want to specifically say that inc5 is continuous, not all Float -> Float functions. Thus, we could have another abstraction, lets call it _value_ class, where we could say that an individual value (function) could be member. We could say something like: class Invertible (f :: a -> a) where invert :: f -> (a -> a) instance Invertible inc5 where invert _ = \x -> x - 5 In many cases this would be too specific. We would like to say, that applying the first argument to `+` returns an invertible function. Something like: instance Invertible (`+` x) where invert (x +) = \y -> y - x We would properly also like to say, that composing two invertible functions results in another invertible function. I guess there are many more examples. This idea, of value classes, do not feel all that novel. Somebody has properly thought about it before, but gave it a different name. If anybody has links to some papers it would be much appreciated. If anybody has some thoughts of the desirability of value class it would also be much appreciated. /Mads Lindstrøm