A VISUAL DEBUGGER FOR PURE PROLOG

This work involves the design and coding of an interpreter for pure Pr olog and building a visual debugger for it. Most of the available Prol og interpreters contain some tracing facilities. They do not incorpora te, however, a comprehensive visual debugger. The interpreter performs the operations of parsing, unification, resolution, and search in a s tate-space representation of the Prolog program. The visual debugger i ncorporates the graphical visualization and the manipulation of the SL D resolution tree. The user visualizes the execution of a pure Prolog program and interacts with the program inside a windowing environment. The program execution may be viewed without interruption or the execu tion can be stopped at any moment in time. At this point the ''snapsho t'' can be scrutinized with the help of break-points and data displays . This software aims itself to those who wish to observe the actual pr ocess of predicate unification, substitution, resolution, and goal mat ching in a Prolog program and to visually interact with the interprete r using a highly friendly and pleasing user interface. An advanced fea ture, referred to as debugging on the tree, provides the user with the ability to insert break-points directly on the SLD tree, to choose th e path of execution, and change the search mode. The resultant search algorithm can be a mixture of depth-first and breadth-first search, av oiding infinite search paths.