string_gymnastics.rb

price_list = "orange = 10p apple = 20p bread = £1.10 tomato = 25p cereal = £2.34"
list = <<-LIST
 list
 orange
 apple
 apple
 orange
 tomato
 cereal
 bread
 orange
 tomato
LIST

class Catalog
  PARSE_REGEX = /(\w+)\s=\s£?([\d.]+)p?/

  def initialize(raw_prices)
    @prices = parse(raw_prices)
  end

  def parse(raw)
    matches = raw.scan(PARSE_REGEX)
    matches.inject({}) do |buffer, match|
      buffer.tap do |hash|
        name = match[0]
        price = coerce_price(match[1])
        hash[name] = price
      end
    end
  end

  def lookup(name)
    @prices[name]
  end

private

  def coerce_price(raw)
    price = raw.include?('.') ? (raw.to_f * 100) : raw
    price.to_i
  end
end

class Basket

  def initialize(raw_list)
    @items = parse(raw_list)
  end

  def parse(raw)
    raw.split.tap { |r| r.shift }
  end

  def each(&block)
    @items.each(&block)
  end

end

class Checkout

  def initialize(prices, basket)
    @prices, @basket = prices, basket
    @total = 0
  end

  def process
    @basket.each do |item|
      @total += @prices.lookup(item)
    end
  end

  def total
    @total
  end

end

catalog = Catalog.new(price_list)
basket = Basket.new(list)
checkout = Checkout.new(catalog, basket)
checkout.process

puts "The price of the shopping list is: £%.2f" % (checkout.total.to_f / 100)