ruby alternative option parser

mdop.rb

#
# simple option parser that supports negative numbers as arguments, because I needed to do that
#
# should mostly be a drop-in replacement for OptionParser's basic usage patterns
#
class MDOP
  
  #
  # class to hold each option's data (including its Proc)
  #
  class MDOption

    attr_reader :short, :long, :desc, :block, :klass

    def initialize(short, long, klass, desc, block)
      @short = short
      @long = long
      if @short.nil? and @long.nil?
        raise ArgumentError.nil("Short name and long name can't both be nil!")
      elsif @short.nil?
        @short = @long
      elsif @long.nil?
        @long = @short
      end
      @klass = klass
      @desc = desc
      @block = block
    end

    def parse(argv_r) # reversed argv
      token = argv_r.pop
      if token.match(@short) or token.match(@long)
        if @klass # if this one has a value
          val = argv_r.pop
          if @klass == Integer # couldn't get a case statement to work here!
            val = val.to_i
          elsif @klass == Float
            val = val.to_f
          elsif @klass == String
          else
            raise ArgumentError.new("I can't read values of class #{@klass.to_s}!")
          end
          @block.call(val)
        else # if it's just a flag
          @block.call
        end
        return true
      else
        argv_r.push(token)
        return false
      end
    end
    
  end

  attr_accessor :banner

  def initialize(banner = nil)
    @banner = banner
    @opts = []
    super
  end

  def to_s
    return banner
  end

  def parse(argv)
    argv_r = argv.reverse
    extra_args = []
    while(argv_r.size > 0)
      found = false
      @opts.each{ |opt|
        if opt.parse(argv_r)
          found = true
          break
        end
      }
      extra_args.push(argv_r.pop) unless found
    end
    return extra_args
  end
  
  def on(*args, &block)
    raise "There's no point in defining an option without a block..." unless block
    if args.size == 4
      on_param(*args, block)
    elsif args.size == 3
      on_noparam(*args, block)
    else
      raise ArgumentError.new("you must supply four or five arguments!")
    end
  end
  
  private

  def on_noparam(short, long, desc, block)
    @opts << MDOption.new(short, long, nil, desc, block)
  end
  
  def on_param(short, long, klass, desc, block)
    @opts << MDOption.new(short, long, klass, desc, block)
  end

end