Parametric Type Classes

Kung Chen, Paul Hudak, Martin Odersky

ACM Conf. on Lisp and Functional Programming, June 1992

We propose a generalization to Haskell's type classes where a class
can have type parameters besides the placeholder variable. We show
that this generalization is essential to represent container classes
with overloaded data constructor and selector operations. We also show
that the resulting type system has principal types and present
unification and type reconstruction algorithms.