cons/car/cdr in ruby

cons.rb

def cons(x, y)
  ->(label) do
    case label
      when :first then x
      when :second then y
      else raise "Argument is neither :first nor :second -- cons"
    end
  end
end

def car(tuple)
  tuple.call(:first)
end

def cdr(tuple)
  tuple.call(:second)
end

pair = cons(1, "a")

puts car(pair) #=> 1
puts cdr(pair) #=> a