Class: Peggy::PEG

Inherits:
Parser show all
Defined in:
lib/peg.rb,
lib/Copy of peg.rb

Overview

Implements the Parser Expression Grammar (PEG), one of several grammars supported.

Defined Under Namespace

Classes: PEGCompiler

Instance Attribute Summary

Attributes inherited from Parser

#debug_flag, #ignore_productions, #parse_results, #source_text

Instance Method Summary collapse

Methods inherited from Parser

#[], #allow?, #check?, #correct_regexp!, #dissallow?, #eof, #ignore?, #literal?, #match?, #parse?, #query?, #regexp?, #string?

Constructor Details

#initialize ⇒ PEG

Returns a new instance of PEG.



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# File 'lib/peg.rb', line 10

def initialize
  super
  build
end

Instance Method Details

#build_prefix(prefix) ⇒ Object 



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# File 'lib/Copy of peg.rb', line 104

def build_prefix prefix
  if sequence.peek
    pos do
      build_suffix prefix.suffix
    end
  elsif sequence.disallow
    neg do
      build_suffix prefix.suffix
    end
  else
    build_suffix prefix.suffix
  end
end

#build_sequence(sequence) ⇒ Object 



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# File 'lib/Copy of peg.rb', line 92

def build_sequence sequence
  if sequence.count('prefix') == 1
    build_prefix sequence.prefix
  else
    each do
      sequence.find_each 'prefix' do |prefix|
        build_prefix prefix
      end
    end
  end
end

#build_suffix(suffix) ⇒ Object 



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# File 'lib/Copy of peg.rb', line 118

def build_suffix suffix
  if suffix.question
    opt do
      build_primary suffix.primary
    end
  elsif suffix.
    neg do
      build_suffix prefix.suffix
    end
  else
    build_suffix prefix.suffix
  end
end

#compile?(text) ⇒ Boolean

PEGCompiler

Returns:

  • (Boolean) 


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# File 'lib/Copy of peg.rb', line 71

def compile? text
  reset!
  compiler = PEGCompiler.new
  raise "Invalid grammar" unless compiler.parse! :grammar, text
  ast = compiler.ast
  ast.find_each 'definition' do |definition|
    send definition.identifier.to_sym do
      if definition.count('sequence') == 1
        build_sequence definition.expression.sequence
      else
        one do
          definition.find_each 'sequence' do |sequence|
            build_sequence sequence
        end
      end
      end
    end
  end
  
private

  def build_sequence sequence
    if sequence.count('prefix') == 1
      build_prefix sequence.prefix
    else
      each do
        sequence.find_each 'prefix' do |prefix|
          build_prefix prefix
        end
      end
    end
  end
  
  def build_prefix prefix
    if sequence.peek
      pos do
        build_suffix prefix.suffix
      end
    elsif sequence.disallow
      neg do
        build_suffix prefix.suffix
      end
    else
      build_suffix prefix.suffix
    end
  end
  
  def build_suffix suffix
    if suffix.question
      opt do
        build_primary suffix.primary
      end
    elsif suffix.
      neg do
        build_suffix prefix.suffix
      end
    else
      build_suffix prefix.suffix
    end
  end

end