Commutative function in Haskell

Question

I want to write a function in haskell which would not mind in what order I provide it its argument, for example, I want to unify these two functions

    reproduce1 :: Male -> Female -> Child
    reproduce2 :: Female -> Male -> Child

by one function 'reproduce'.

Answer 1

You can do this using a multi-parameter type class.

{-# LANGUAGE MultiParamTypeClasses #-}

class Reproduce x y where
  reproduce :: x -> y -> Child

instance Reproduce Male Female where
  reproduce = reproduce1

instance Reproduce Female Male where
  reproduce = reproduce2

However, I'm curious about why you would want to do this.