My work on the Uncle Bob bowling kata.

game.rb

class Game
  def roll(*pins)
    (@rolls ||= []).push *pins
  end

  def score
    scores.inject(:+)
  end

  def scores
    [].tap do |frame_scores|
      10.times do
        score, taken = score_frame(@rolls)
        @rolls = @rolls.drop(taken)

        frame_scores << score
      end
    end
  end

  def score_frame(rolls)
    rolls_for_scoring, rolls_in_this_frame = case frame_kind(rolls)
    when :strike then [3, 1]
    when :spare  then [3, 2]
    when :open   then [2, 2]
    end

    [rolls.take(rolls_for_scoring).inject(:+), rolls_in_this_frame]
  end

  def frame_kind(rolls)
    first, second = rolls
    return :strike if first          == 10
    return :spare  if first + second == 10
    return :open
  end
end

game_spec.rb

require 'spec_helper'
require 'lib/game'

describe Game do
  let(:game) { described_class.new }
  def roll(*rolls)
    game.roll(*rolls.flatten)
  end

  def frames(n, frame = [0, 0])
    Array.new(n, frame)
  end

  it "scores twelve strikes as 300" do
    roll frames(12, [10])
    expect(game.score).to eq 300
  end

  it "scores ten gutter frames as 0" do
    roll frames(10)
    expect(game.score).to eq 0
  end

  it "scores ten open frames as their sums" do
    roll frames(10, [2, 3])
    expect(game.score).to eq 50
  end

  it "scores a spare as 10 plus next roll" do
    roll 4, 6, 7, 3, frames(8)
    expect(game.scores.first).to eq 17
  end

  it "scores a strike as 10 plus next two rolls" do
    roll 10, 4, 6, 7, 3, frames(7)
    expect(game.scores.first).to eq 20
  end
end