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

In Haskell, every "function" takes exactly one argument. What looks like a "multi-argument" function is actually a function that takes one argument and returns another function which takes the rest of the arguments. So in that sense all functions have arity 1.