Abstract

The semantics of constraint logic programming languages with coroutining facilities (e.g., "freeze," suspension, residuation) cannot be fully declarative. Thus, an operational semantics has to be taken as the defining one. We give a formal operational semantics for a Prolog-like language with cut and entailment-based conditional. Our approach is derived from those used for concurrent calculi. We use congruence laws and tree-rewriting rules to define the semantics. We model the execution of a program by a sequence of abstract-tree rewriting steps. This semantics serves as a defining tool for the language designer and as the interface between the language designer and implementor; it allows the programmer to check his intuition with a formal execution model and it gives him a performance measure for the execution of programs. We have used the semantics to make precise, for the first time, the critical interaction between sequential execution (including backtracking and cut pruning) and c...

Citations