A unified system of parameterization for programming languages

Abstract

Current programming languages tend to have several different mechanisms that provide parameterization. For example, most languages have both variables, which communicate parameter values primarily within routines, and procedure invocations, which communicate parameter values primarily between routines. Depending on the situation, one mechanism or the other must be used. The mechanisms also tend to involve more than just parameterization; a procedure call, for example, also implies a transfer of control. The principle of orthogonal design for programming languages suggests that it would be desirable to have a single parameterization mechanism that can be used in all situations and that doesn't affect anything but parameterization. We consider what properties such a mechanism would have to have, concluding, for example, that parameters must be nameable, and, more importantly, that all the parameterization facilities that are available in language expressions must also be available in data objects. These properties, in turn, put requirements on the underlying semantic structure of a programming language. We develop a formal system of parameterization with those properties. The system has theoretical power equivalent to the lambda calculus, and is about the same size. It can serve as the basis of all parameterization in a functional programming language, being able to express constructions like procedure call, variable binding, mutual recursion, and module linkage. In addition to being able to express the common parameterization constructions, the uniformity and universality of the system offer improved modularity, extensibility, and simplicity. It is especially useful for applications that need to create new code at runtime.