That's not always true, rank-1 polymorphic functions (i.e. functions polymorphic in their argument) don't usually require type annotations. Higher-rank polymorp

That's not always true, rank-1 polymorphic functions (i.e. functions polymorphic in their argument) don't usually require type annotations. Higher-rank polymorphic functions though do generally require them, because without the annotations type inference is undecidable in the general case for such functions. For example: pair x y = (x, y) This function creates a pair for any two types, and doesn't require any annotations.