Implementation and applications of Scott's logic for computable functions

Abstract

The basis for this paper is a logic designed by Dana Scott [1] in 1969 for formalizing arguments about computable functions of higher type. This logic uses typed combinators, and we give a more or less direct translation into typed λ-calculus, which is an easier formalism to use, though not so easy for the metatheory because of the presence of bound variables. We then describe, by example only, a proof-checker program which has been implemented for this logic; the program is fully described in [2]. We relate the induction rule which is central to the logic to two more familiar rules - Recursion Induction and Structural Induction - showing that the former is a theorem of the logic, and that for recursively defined structures the latter is a derived rule of the logic. Finally we show how the syntax and semantics of a simple programming language may be described completely in the logic, and we give an example of a theorem which relates syntactic and semantic properties of programs and which can be stated and proved within the logic.