functional_array.rb

class FunctionalArray
  attr_reader :head
  attr_reader :tail

  def initialize(*items)
    @head = items.first
    tail = items[1..-1]
    @tail = (tail.count > 0) ? self.class.new(items[1..-1]) : []
  end
  
  def count
    1 + tail.count
  end

  def inject(initial, &block)
    memo = block.call(initial, head)
    if tail.count > 0
      tail.inject(memo, &block)
    else
      memo
    end
  end

  def map(&block)
    reply = inject([]) do |memo, item|
      [ *memo, block.call(item) ]
    end
    self.class.new(reply)
  end
end