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RubyPeg helps you to create readable & debug-able Parsing Expression Grammars (PEGs) in ruby
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LICENCE
README.md
rakefile.rb
rubypeg.gemspec

README.md

RubyPeg

RubyPeg helps you to create readable Parsing Expression Grammars (PEG) in ruby.

This software is (c) 2010 Green on Black Ltd and distributed under the open source MIT licence. (See LICENCE for the wording).

If you like this code, employ us: http://www.greenonblack.com

An example

class Arithmetic < RubyPeg

  def root
    arithmetic
  end

  def arithmetic
    node :arithmetic do
      one_or_more { expression } && ignore { terminal(/\z/) }
    end
  end

  def expression
    subtraction || addition || division || multiplication || brackets || number
  end

  def brackets
    node :brackets do
      ignore { terminal("(") } && spacing && expression && spacing && ignore { terminal(")") }
    end
  end

  def multiplication
    node :multiplication do
      (brackets || number) && spacing && ignore { terminal("*") } && spacing && expression
    end
  end

  def division
    node :division do
      (brackets || number) && spacing && ignore { terminal("/") } && spacing && expression
    end
  end

  def addition
    node :addition do
      (brackets || number) && spacing && ignore { terminal("+") } && spacing && expression
    end
  end

  def subtraction
    node :subtraction do
      (brackets || number) && spacing && ignore { terminal("-") } && spacing && expression
    end
  end

  def number
    terminal(/[-+]?[0-9]+\.?[0-9]*([eE][-+]?[0-9]+)?/)
  end

  def spacing
    ignore { terminal(/[ \t]*/) }
  end

end

Arithmetic.parse("(1+1)+2").to_ast 
# [:arithmetic,[:addition,[:brackets,[:addition,'1','1']],'2']]
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