Program Templates: Expression Templates Applied to Program Evaluation

The C++ language provides a two-layer execution model: static execution of meta-programs and dynamic execution of resulting programs. The Expression Templates technique takes advantage of this dual execution model through the construction of C++ types expressing simple arithmetic formulas. Our intent is to extend this technique to a whole programming language. The Tiger language is a small, imperative language with types, variables, arrays, records, flow control structures and nested functions. The first step is to show how to express a Tiger program as a C++ type. The second step concerns operational analysis which is done through the use of meta-programs. Finally an implementation of our Tiger evaluator is proposed. Our technique goes much deeper than the Expression Templates one. It shows how the generative power of C++ meta-programming can be used in order to compile abstract syntax trees of a fully featured programming language.