Class: RDParser

Inherits:
Object
  • Object
show all
Defined in:
lib/asciitracker/rdparser.rb

Overview

Subject: ***Re: [SOLUTION] Dice Roller (#61)* From: *Dennis Ranke *<mail exoticorn.de> Date: Mon, 9 Jan 2006 06:53:10 +0900 References: 174521 </cgi-bin/scat.rb/ruby/ruby-talk/174521> 174811 </cgi-bin/scat.rb/ruby/ruby-talk/174811> In-reply-to: 174811 </cgi-bin/scat.rb/ruby/ruby-talk/174811>

Hi,

here is my second solution. Quite a bit longer, but a lot nicer. For this I implemented a simple recursive descent parser class that allows the tokens and the grammar to be defined in a very clean ruby syntax. I think I’d really like to see a production quality parser(generator) using something like this grammar format.

Defined Under Namespace

Classes: LexToken, Rule

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(&block) ⇒ RDParser

Returns a new instance of RDParser.



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# File 'lib/asciitracker/rdparser.rb', line 22

def initialize(&block)
  @lex_tokens = []
  @rules = {}
  @start = nil
  instance_eval(&block)
end

Instance Attribute Details

#pos ⇒ Object

Returns the value of attribute pos.



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# File 'lib/asciitracker/rdparser.rb', line 19

def pos
  @pos
end

#rules ⇒ Object (readonly)

Returns the value of attribute rules.



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# File 'lib/asciitracker/rdparser.rb', line 20

def rules
  @rules
end

Instance Method Details

#expect(tok) ⇒ Object 



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# File 'lib/asciitracker/rdparser.rb', line 64

def expect(tok)
  t = next_token
  if @pos - 1 > @max_pos
    @max_pos = @pos - 1
    @expected = []
  end
  return t if tok === t
  @expected << tok if @max_pos == @pos - 1 && !@expected.include?(tok)
  return nil
end

#next_token ⇒ Object 



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# File 'lib/asciitracker/rdparser.rb', line 59

def next_token
  @pos += 1
  return @tokens[@pos - 1]
end

#parse(string) ⇒ Object 



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# File 'lib/asciitracker/rdparser.rb', line 29

def parse(string)
  @tokens = []
  until string.empty?
    raise "unable to lex '#{string}" unless @lex_tokens.any? do |tok|
#puts "match(#{string}) <- (#{tok})"
      match = tok.pattern.match(string)
      if match
          s_tok = match.to_s
puts "(#{s_tok})" unless /^\s+$/.match(s_tok)
#puts "<<< #{s_tok} | #{tok.pattern} >>>"
        @tokens << tok.block.call(s_tok) if tok.block
        string = match.post_match
#puts "<<<#{s_tok}|||#{match.post_match}>>>"
        true
      else
        false
      end
    end
  end
  @pos = 0
  @max_pos = 0
  @expected = []
  result = @start.parse
  if @pos != @tokens.size
    raise "Parse error. expected: '#{@expected.join(', ')}', found 
'#{@tokens[@max_pos]}'"
  end
  return result
end