ML with extended pattern matching and subtypes

Abstract

We extend a fragment of the programming language Standard ML by incorporating a more general form of record pattern matching and providing for user-declared subtypes. Together, these two enhancements may be used to support a restricted object-oriented programming style. In keeping with the framework of Standard ML, we present typing rules for the language, and develop an efficient type inference algorithm. We prove that the algorithm is sound with respect to the typing rules, and that it infers a most general typing for every typable expression.