The Expanded Term Language as a Functional Programming Language

Abstract

The Expanded Term Language (ET) is a notation for expressing constructions, which are essentially data structures and algorithms. Thus ET may be regarded in computer science terms as a functional programming language, with the Term Language as its machine code and Protologic and Expanded Protologic as its correctness calculus. In this chapter I shall discuss the use of ET as a practical programming language, in comparison with other functional languages such as LISP (McCarthy, 1960), FP (Backus, 1978) and its successor FL (Backus, Williams & Wimmers, 1990), Standard ML (Milner, Tofte & Harper, 1990; Milner & Tofte, 1991), Miranda (Holyer, 1991), Haskell (ACM, 1992; Davie, 1992), and Hope (Burstall, MacQueen & San-nella, 1980). (See also Chapter 13 for a comparison of ET with λ-calculus.) The issues to be considered for each language are

• correctness proofs

• functions as ‘first-class’ objects

• data types, including polymorphism and overloading

• pattern matching

• lazy data structures, streams and interactive programming

• modularity and programming in the large

• efficiency of execution.