A Transitional Semantics of Full Prolog

A structural operational semantics is given to full Prolog, including cut and negation. Backtracking is implemented through lookahead and requires no auxiliary structures, besides the goal and the accumulated substitution. A concurrent version of this semantics is also outlined. Keywords: Prolog, Structural Operational Semantics, Transition Systems, Lookahead, Concurrency. 1 Introduction The semantics of many programming languages has been defined following the approach advocated by Plotkin in [9], called Structural Operational Semantics, SOS for short. The idea is to associate a transition system, i.e., an oriented graph, with a language. A node represents the state of the abstract machine running the language, usually a pair hprogram, datai. A transition describes the (atomic) activity that makes the state change, in a single step. A basic point is that transitions are defined in a logical style by inference rules, inducing on the syntactic structure of programs. The advantages of..