Haskell: Function to determine the arity of functions?

Question

Is it possible to write a function arity :: a -> Integer to determine the arity of arbitrary functions, such that

> arity map
2
> arity fol         


        

Answer 1

If id has arity 1, shouldn't id x have arity 0? But, for example, id map is identical to map, which would has arity 2 in your example.

Have the following functions the same arity?

f1 = (+)
f2 = (\x y -> x + y)
f3 x y = x + y

I think your notion of "arity" is not well defined...