Functional Programming Languages

Abstract

Functional programming languages are a class of languages designed to reflect the way people think mathematically, rather than reflecting the underlying machine. Functional languages are based on the lambda calculus, a simple model of computation, and have a solid theoretical foundation that allows one to reason formally about the programs written in them. The most commonly used functional languages are Standard ML, Haskell, and “pure” Scheme (a dialect of LISP), which, although they differ in many ways, share most of the properties described here. For a complete description of these languages and of functional programming in general, see Bird and Wadler [1988], Paulson [1991], Sussman and Abelson [1985], Hudak et al. [1992], Milner et al. [1990], Artificial Intelligence Laboratory [1992], and Hudak [1989]. In contrast to the usual imperative languages (e.g., C, Fortran, and Ada), in which variables represent cells in memory that can be modified using the assignment operator 5 (or :5), functional languages view the use of the 5 operator as an expression of an equation. For example, if a functional program contains the declaration