Type Checking Type Classes
Tobias Nipkow, Christian Prehofer
We study the type inference problem for a system with type classes as in the
functional programming language Haskell. Type classes are an extension of
ML-style polymorphism with overloading. We generalize Milner's work on
polymorphism by introducing a separate context constraining the type
variables in a typing judgement. This leads to simple type inference systems
and algorithms which closely resemble those for ML. In particular we present
a new unification algorithm which is an extension of syntactic unification
with constraint solving. The existence of principal types follows from an
analysis of this unification algorithm.
author="Tobias Nipkow and Christian Prehofer",
title="Type Checking Type Classes",
booktitle="Proc.\ 20th ACM Symp.\ Principles of Programming Languages",
A revised version appeared in
Journal of Functional Programming.