ad hoc vs. parametric polymorphism

polymorphisms.hs

-- The key difference between parametric polymorphism and overloading (aka ad-hoc
-- polymorphism) is that parameteric polymorphic functions use one algorithm to 
-- operate on arguments of many different types, whereas overloaded functions may 
-- use a different algorithm for each type of argument.

-- John Mitchell, Concepts in Programming Languages
-- http://stackoverflow.com/a/13043262/382982

-- ad hoc/constrained => typeclasses
plus :: (Num a) => a -> a -> a 
plus a b = (+) a b
  
-- parametric => generics
swap :: (A, B) -> (B, A)
swap (a, b) = (b, a)