Scheme: Implementing cons, car, and cdr

I'm going through Structure and Interpretation of Computer Programs per the recommendation of my buddy Mike Cheponis. I'm really enjoying it.

I always thought cons, car, and cdr were so low-level that they had to be builtins. However, interestingly enough, SICP shows how they could be implemented using a closure:

(define (my-cons a b)
  (lambda (pick)
    (cond ((= pick 1) a)
          ((= pick 2) b))))

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

It's kind of silly, but it also works in Python:

def cons(a, b):

    def list(pick):
        if pick == 1:
            return a
        elif pick == 2:
            return b
        else:
            raise ValueError

    return list

def car(list):
    return list(1)

def cdr(list):
    return list(2)

Neat!

It's easy to see how to extend this in Scheme to have "objects" with any number of memebers, although I'm sure it's not very efficient.

By the way, I really like DrScheme. It's relatively modern and very friendly.