Static Type Inference in a Dynamically Typed Language

Abstract

We present a type inference system for FL based on an operational, rather than a denotational, formulation of types. The essential elements of the system are a type language based on regular trees and a type inference logic that implements an abstract interpretation of the operational semantics of FL. We use a non-standard approach to type inference because our requirements---using type information in the optimization of functional programs---differ substantially from those of other type systems. 1 Introduction Compilers derive at least two benefits from static type inference: the ability to detect and report potential run-time errors at compile-time, and the use of type information in program optimization. Traditionally, type systems have emphasized the detection of type errors. Statically typed functional languages such as Haskell [HWA*88] and ML [HMT89] include type constraints as part of the language definition, making some type inference necessary to ensure that type constraints ...