A GRAPHICAL DEBUGGER FOR PROLOG

Abstract

This thesis presents the implementation of DEWLAP (DEbugging With Logical APplications), a graphical debugger for Prolog. DEWLAP is the first Prolog debugger to present program executions in an entirely graphical fashion. Instead of showing source listings for program tracing, DEWLAP displays the execution as a dynamically-changing tree. This tree shows not only the currently-active sequence of goals, but also the entire execution history. In this way, the user is provided with a much more complete view of the execution than is possible with other debuggers for Prolog or for any other language. A need for a compromise between clarity of high-level information and accessibility of low-level detail arises in a number of contexts. This problem is solved in DEWLAP by giving the user the tools needed to tailor displays and to focus attention on those parts of the execution tree which are of current interest.