An extension of HM(X) with bounded existential and universal data-types

Abstract

We propose a conservative extension of HM( X ), a generic constraint-based type inference framework, with bounded existential (a.k.a. abstract) and universal (a.k.a. polymorphic) data-types. In the first part of the article, which remains abstract of the type and constraint language (i.e. the logic X ), we introduce the type system, prove its safety and define a type inference algorithm which computes principal typing judgments. In the second part, we propose a realistic constraint solving algorithm for the case of structural sub-typing, which handles the non-standard construct of the constraint language generated by type inference: a form of bounded universal quantification.