antlr.rb

ANTLR(ANother Tool for Language Recognition)它是这样的一种工具

# [The "BSD licence"]
# Copyright (c) 2005 Martin Traverso
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in the
#    documentation and/or other materials provided with the distribution.
# 3. The name of the author may not be used to endorse or promote products
#    derived from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
# OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
# IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
# NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

require 'tmpdir'
require 'tempfile'
require 'stringio'
require 'fileutils'

include FileUtils

class Grammar
	def self.compile(grammar)
		md = /(\w+)/.match(grammar)
		raise "Cannot find starting rule" if md.nil?
		top_rule = md[1]

		type = top_rule == top_rule.upcase ? "lexer" : ""

		name = "Grammar#{Time.now.to_i}#{rand(1000)}"

		grammar = <<-GRAMMAR
			#{type} grammar #{name};
			options { language = Ruby; }

			#{grammar}
		GRAMMAR

        tempfile = Tempfile.new("antlr")
        dirname = tempfile.path + ".dir"
        Dir.mkdir(dirname)

		grammar_class = nil

        cd(dirname) do
			# write the grammar to a file
			File.open("#{name}.g", "w") { |f| f.puts grammar }

	        # run antlr
		    `java -cp #{ENV['CLASSPATH']} org.antlr.Tool #{name}.g`

				class_name = name + (type == "lexer" ? "Lexer" : "Parser")

            load(dirname + "/#{class_name}.rb")

            grammar_class = Class::const_get(class_name)

            # delete created files
            Dir.new(dirname).each { |file|
                rm_f(file) if file != ".." && file != "."
            }
        end

        Dir.delete(dirname)

        if type == "lexer"
            Lexer.new(grammar_class)
        else
            Parser.new(grammar_class, top_rule)
        end
    end

    class Lexer
        def initialize(grammar)
            @grammar = grammar
        end

        def parse(input)
            parser = @grammar.new(input)

            tokens = []
            loop do
                token = parser.next_token
                break if token == :EOF
                tokens << token
            end

            tokens
        end
    end

    class Parser
        def initialize(grammar, top_rule)
            @grammar = grammar
            @top_rule = top_rule
        end

        def parse(input)
            @grammar.new(input).send @top_rule
        end
    end
end