Just a very simple program from SICP book both in Lisp and Ruby to show how much more elegant the code will be when the philosophy of "Code as Data" exist in a language!

pair-car-cdr.lisp

(define make-pair (a, b)
 (lambda (pick)
  (cond (= pick 1) a)
  (cond (= pick 2) b)))

(define car (x) (x 1))
(define cdr (x) (x 2))

pair_car_cdr.rb

def make_pair(a, b)
  lambda do |pick|
    case pick
      when 1
        return a
      when 2
        return b
    end
  end
end

def car(picker)
  picker.call(1)
end

def cdr(picker)
  picker.call(2)
end