y_parser.treetop

grammar Y

  rule topmost
    expression*
    {
      def bnf
        self.elements.each {
          |p| 
          puts "#{p.rule_name.text_value} : #{p.rewrite_list}" 
        }
      end
    }
  end
  
  rule expression
    white_space? rule_name white_space? ':' rewrite_list ';' space?
  end
  
  rule rewrite_list
    rule_list:(space? rewrite_name)* space?
    {
      def to_s
        rule_list.elements.collect {|rew| rew.rewrite_name.text_value }.join(" ").gsub("| ", "|\n\t")
      end
    }
  end
  
  rule rule_name
    [a-zA-Z] [a-zA-Z0-9_]*
  end
  
  rule rewrite_name
    identifier / quoted_identifier
  end
  
  rule identifier
    [%|a-zA-Z] [a-zA-Z0-9_]*
  end
  
  rule quoted_identifier
    '\'' [^\']* '\''
  end

  rule space
    (white_space / c_block)* 
    {
      def value
        nil
      end
    }
  end
  
  rule white_space
    [\s]+
  end
  
  rule c_block
    '{' non_curly (c_block non_curly)* '}'
  end
  
  rule non_curly
    [^{}]*
  end
   
end