THE TRANSPARENT PROLOG MACHINE (TPM) - AN EXECUTION MODEL AND GRAPHICAL DEBUGGER FOR LOGIC PROGRAMMING

An augmented AND/OR tree representation of logic programs is presented as the basis for an advanced graphical tracing and debugging facility for PROLOG. An extension of our earlier work on 'retrospective zooming', this representation offers several distinct advantages over existing tracing and debugging facilities. By enhancing AND/OR trees to include 'status boxes' rather than simple 'nodes', it is possible to display both a long-distance view of execution and the full details of clause-head matching. Graphical 'collapsing' techniques enable the model to deal with user-defined abstractions, higher-order predicates such as setof, and definite-clause grammars. The current implementation runs on modern graphics workstations and is written in PROLOG.