Software visualization of LR parsing and synthesized attribute evaluation

Visual YACC is a tool that automatically creates visualizations of the YACC LR parsing process and synthesized attribute computation. The Visual YACC tool works by instrumenting a standard YACC grammar with graphics calls tha t draw the appropriate data structures given the current actions by the par ser, The new grammar is processed by the YACC tools and the resulting parse r displays the parse stack and parse tree for every step of the parsing pro cess of a given input string. Visual YACC was initially designed to be used in compiler construction cour ses to supplement the teaching of parsing and syntax directed evaluation. W e have also found it to be useful in the difficult task of debugging YACC g rammars. In this paper, we describe this tool and how it is used in both co ntexts. We also detail two different implementations of this tool: one that produces a parser written in C with calls to Motif; and a second implement ation that generates Java source code. Copyright (C) 1999 John Wiley & Sons , Ltd.