Dice rolling expressions in Ruby w/ Treetop

dexp.rb

require 'forwardable'

module Dexp
  class Roll
    attr_reader :count, :sides, :modifier

    def initialize(count, sides, modifier)
      @count, @sides, @modifier = count, sides, modifier
    end

    def results
      modifier.call(RollProxy.new(self))
    end
  end

  class RollProxy
    extend Forwardable

    def initialize(roll)
      @roll = roll
      @array = Array.new(roll.count) { rand(roll.sides) }
    end
    def_delegators :@array, :max, :min, :sort

    def sum
      @array.inject(0) {|a,e| a + e }
    end

    def open
      @array += @roll.results if @array.any? {|e| e == @roll.sides - 1 }

      return @array
    end

    def inspect
      @array.inspect
    end
  end

  module IntegerNode
    def value
      text_value.to_i
    end
  end

  def OperatorNode(op)
    return Module.new.tap {|mod|
      mod.send(:define_method, :value) {
        lambda {|a|
          a.map {|e| e.send(op, number.value)}
        }
      }
    }
  end
end

dexp.treetop

require 'dexp'

grammar Dice
  rule expression
    count:(number?) 'd' sides modifier {
      def roller
        Dexp::Roll.new(count.value, sides.value, modifier.value)
      end
    }
  end

  rule number
    [1-9] [0-9]* <Dexp::IntegerNode>
  end

  rule modifier
    '+' number <Dexp::OperatorNode(:+)>
    /
    '-' number <Dexp::OperatorNode(:-)>
    /
    function
    /
    '' {
      def value
        lambda {|a| a }
      end
    }
  end

  rule function
    '.' fun:('max' / 'min' / 'sum' / 'sort' / 'open') {
      def value
        lambda {|a| a.send(fun.text_value.to_sym) }
      end
    }
  end

  rule sides
    ('100' / '20' / '12' / '10' / '8' / '6' / '4' / '2') <Dexp::IntegerNode>
  end
end