GraphViz::Parse::Yacc - Visualise grammars


  use GraphViz::Parse::Yacc;

  # Pass in a file generated via yacc -v
  my $graph = GraphViz::Parse::Yacc->new('Yacc.output');
  print $g->as_png;


This module makes it easy to visualise Parse::Yacc grammars. Writing Parse::Yacc grammars is tricky at the best of times, and grammars almost always evolve in ways unforseen at the start. This module aims to visualise a grammar as a graph in order to make the structure clear and aid in understanding the grammar.

Rules are represented as nodes, which have their name on the left of the node and their productions on the right of the node. The subrules present in the productions are represented by edges to the subrule nodes.

Thus, every node (rule) should be connected to the graph - otherwise a rule is not part of the grammar.

This uses the GraphViz module to draw the graph. Thanks to Damian Conway for the original idea.



This is the constructor. It takes one mandatory argument, which is a filename of the output file generated by running "yacc -v " on the grammar file. For example, if your Parse::Yacc grammar file is called "calc.yp", you would run "yacc -v calc.y" and pass in "calc.output" as an argument here. A GraphViz object is returned.

  # Pass in a file generated via yacc -v
  my $graph = GraphViz::Parse::Yacc->new('Yacc.output');
  print $g->as_png;


The grammar can be visualised in a number of different graphical formats. Methods include as_ps, as_hpgl, as_pcl, as_mif, as_pic, as_gd, as_gd2, as_gif, as_jpeg, as_png, as_wbmp, as_ismap, as_imap, as_vrml, as_vtx, as_mp, as_fig, as_svg. See the GraphViz documentation for more information. The two most common methods are:

  # Print out a PNG-format file
  print $g->as_png;

  # Print out a PostScript-format file
  print $g->as_ps;


Leon Brocard <>


Copyright (C) 2001, Leon Brocard

This module is free software; you can redistribute it or modify it under the Perl License, a copy of which is available at