# Usage

## Compiling Racc grammer file

To compile Racc grammer file, simply type:

      $ racc parse.y

This creates ruby script file "parse.tab.y". -o option changes this.

## Creating Parser with Racc

If you want your own parser, you have to write grammer file. A grammer file contains name of parser class, grammer the parser can parse, user code, and any.
When writing grammer file, yacc's knowledge is helpful. If you have not use yacc, also racc is too difficult.

Here's example of Racc grammer file.

    class Calcparser

    rule
      target: exp { print val[0] }

      exp: exp '+' exp
         | exp '*' exp
         | '(' exp ')'
         | NUMBER
    end

Racc grammer file is resembles to yacc file. But (of cource), action is Ruby code. yacc's $$ is 'result', $0, $1... is an array 'val', $-1, $-2... is an array '_values'.

Then you must prepare parse entry method. There's two types of racc's parse method, "do_parse()" and "yyparse()".
"do_parse()" is simple. it is yyparse() of yacc, and "next_token()" is yylex(). This method must returns an array like [TOKENSYMBOL, ITS_VALUE]. EOF is [false, false]. (token symbol is ruby symbol (got by String#intern) as default. If you want to change this, see grammer reference.
"yyparse()" is little complecated, but useful. It does not use "next_token()", it gets tokens from any iterator. For example, "yyparse(obj, :scan)" causes calling obj#scan, and you can return tokens by yielding them from obj#scan.

When debug, "-v" or/and "-g" option is helpful. "-v" causes creating verbose log file (.output). "-g" causes creating "Verbose Parser". Verbose Parser prints internal status when parsing. But it is not automatic. You must use -g option and set @yydebug true to get output. -g option only creates verbose parser.

### re-distributing Racc runtime

A parser, which is created by Racc, requires Racc runtime. You should re-distribute Racc runtime with your parser. It can be done by using '-E' option.

      racc -E myparser.y

creates myparser.tab.rb which includes racc runtime. Only you must do is to distribute parser file (.rb).

Note: parser.rb is LGPL but your parser is not. You own parser is completely yours.

Copyright (c) 1999-2001 Minero Aoki <aamine@cd.xdsl.ne.jp>