Plus / Sandwich solution

plus.rb

def plus(num)
  (1..num).to_a.map {|x| yield(x) }.join
end

p plus(3) { "ding" }
p plus(3) { |x| "...#{x}" }
p plus(5) { |x| (x + 2).to_s }


def sandwich(layers = 1, &block)
  if (layers == 0)
    "bread"
  else
    [sandwich(layers - 1, &block), yield, "bread"].join(", ")
  end
end

p sandwich { "meat" }
p sandwich(2) { "cheese" }