A Practical Soft Type System for Scheme

Soft typing is a generalization of static type checking that accommodates both dynamic typing and static typing in one framework. A soft type checker infers types for identifiers and inserts explicit run-time checks to transform untypable programs to typable form. Soft Scheme is a practical soft type system for R4RS Scheme. The type checker uses a representation for types that is expressive, easy to interpret, and supports efficient type inference. Soft Scheme supports all of R4RS Scheme, including uncurried procedures of fixed and variable arity, assignment, and continuations