Programming Research Group Technical Monograph PRG-106

Mark Philip Jones

DPhil thesis July 1992, 176 pages, ISBN 0-902928-83-X

This thesis describes a type system that combines ML-style polymorphism with a general approach to overloading. The central idea is to use qualified types that include predicates and restrict the set of types at which an object can be used to particular instances of a polymorphic type. Different applications of qualified types can be obtained by changing the underlying system of predicates. We illustrate this with examples including type classes, explicit subtyping and extensible records.

A description of the implementation of type classes in Haskell and Gofer, an experimental system developed by the author, is added.