Debugging

If you compile the generated D source file with

dmd -debug -debug=parser parser.d

it will output verbose progress information during parsing. For an LR parser, that output is similar to the detailed error information. See the section on error handling for details.

Adding -debug=lexer will additionally print the portion of the input that has been matched by the whitespace grammar in each step.

-debug=nonfatal will print error messages of non-fatal errors. Non-fatal are errors if they occur in an ambiguous situation, where the parser has multiple paths that can lead to a correct parse tree.

Besides the statistics printed during generation of the parser, APaGeD can generate additional information about your grammar and the parser that is useful when debugging a grammar.

The -g command line option prompts APaGeD to output a compact, numbered listing of all lexemes and production rules, which is also useful as an export for documentation.

-a prints the LALR(1) automaton - all states, all LALR(1) entries, all transitions - this can get pretty lenghty. But if in doubt, it's the definitive reference for the parser's behaviour.

-t prints the LALR(1) action and goto tables formatted in HTML. Note that some browsers may have problems with very large tables. On the other hand, beyond a certain size, the tables cease to being helpful anyway.