Fast decompilation of compiled Prolog clauses

Abstract

Serious Prolog implementations in recent years have been primarily compiler-based, nearly all of which are founded on the abstract instruction set of Warren [1983]. The performance achieved by such implementations greatly outstrips that attainable in interpreter-based systems. Unfortunately, the sophistication of these compiler-based environments is often inferior to environments of interpreter-based systems to the extent that a “compatible” interpreter is often required for serious software development. Among the deficiencies of these environments, database operations such as assert, retract, and clause seem to be particularly afflicted. In addition, the ability to debug compiled code has been either non-existent or at best, very constrained.

Unlike compiler technology of many traditional languages, there is little reason for this to be the case in Prolog. An efficient implementation of retract, listing, and clause by decompilation of compiled clause code is the subject of this paper. Techniques used in the implementation of the decompilation process have also proven useful in the implementation of the standard four port debugger found in many Prolog systems.

This work supported in part by U.S. Air Force contract number F30602-81-C-0169.