gistfile1.rb

    kitchen = SafeGrillDecorator.new(
      :kitchen => ExposingDecorator.new(
        :expose => [:strawberry_fluff,:peanut_butter, :bread, :knife],
        :kitchen => UnsafeBareKitchen.new))

    sandwich_maker = SandwichMaker.new

    possible_sandwich = sandwich_maker.
      collect_knife(kitchen).
      with_that(:collect_bread).
      with_that(:collect_strawberry_fluff).
      with_that(:collect_peanut_butter).
      with_that(:spread_strawberry_fluff).
      with_that(:grill)

    decider = EitherDecider.new(possible_sandwich)
    puts decider.on_failure(&:message).on_success(&:payload)

    class UnsafeBareKitchenKitchen
      def initialize(values = {})
        @exposing = values[:exposing] || []
        @ingredients = values[:ingredients] || []
      end

      def exposing(item)
        Failure.new("We don't got #{item} 'round here.")
      end

      def merge_ingredients(first, second)
        new_ingredients = @ingredients-[first,second]+["#{first} and #{second}"]
        Success.new(cloning(:ingredients => new_ingredients))
      end

      def grill
        raise "Kitchen caught fire."
      end

      def to_s
        @ingredients.inspect
      end

      def cloning(additions = {})
        new_params = {
          :exposing => @exposing,
          :ingredients => @ingredients
        }.merge(additions))
        UnsafeBareKitchenKitchen.new(new_params)
      end
    end

    class ExposingDecorator
      def initialize(values = {})
        @kitchen = values[:kitchen].cloning(values)
        @to_expose = values[:expose]
        @exposing = values[:exposing]
      end

      def exposing(item)
        if @to_expose.include?(item)
          Success.new(cloning(:exposing => @exposing+[item]))
        else
          @kitchen.exposing(item)
        end
      end

      def cloning(additions = {})
        new_kitchen = @kitchen.cloning(additions)
        new_params = {:kitchen => new_kitchen}.merge(additions)
        ExposingDecorator.new(new_params)
      end
    end

    class SafeGrillDecorator
      def initialize(values = {})
        @kitchen = values[:kitchen].cloning(values)
        @ingredients = values[:ingredients]
      end

      def grill
        new_ingredients = @ingredients.map{|i| "grilled #{i}"}
        Success.new(cloning(:ingredients => new_ingredients))
      end

      def cloning(additions = {})
        new_kitchen = @kitchen.cloning(additions)
        new_params = {:kitchen => new_kitchen}.merge(additions)
        SafeGrillDecorator.new(new_params)
      end
    end

    class SandwichMaker
      def collect_knife(kitchen)
        kitchen.exposing(:knife)
      end

      def collect_bread(kitchen)
        kitchen.exposing(:bread)
      end

      def collect_strawberry_fluff(kitchen)
        kitchen.exposing(:strawberry_fluff)
      end

      def collect_peanut_butter(kitchen)
        kitchen.exposing(:peanut_butter)
      end

      def spread_strawberry_fluff(kitchen)
        kitchen.merge_ingredients(:bread, :strawberry_fluff)
      end

      def grill(kitchen)
        ExceptionWrapper.new { kitchen.grill(:bread_strawberry_fluff) }
      end
    end