A practical soft type system for scheme

Abstract

Asoft type systeminfers types for the procedures and data structures of dynamically typed programs. Like conventional static types, soft types express program invariants and thereby provide valuable information for program optimization and debugging. A soft typecheckeruses the types inferred by a soft type system to eliminate run-time checks that are provably unnecessary; any remaining run-time checks are flagged as potential program errors.Soft Schemeis a practical soft type checker for R4RS Scheme. Its underlying type system generalizes conventional Hindley-Milner type inference by incorporating recursive types and a limited form of union type. Soft Scheme accommodates all of R4RS Scheme including uncurried procedures of fixed and variable arity, assignment, and continuations.