California State University, Fullerton - CPSC 439 - Exercise 8.10 in Scheme

zip.scm

(define PAIR cons)
(define HEAD car)
(define TAIL cdr)
(define ISEMPTY null?)

(define reverse
  (lambda (l result)
    (if (ISEMPTY l)
        result
        (reverse (TAIL l) (PAIR (HEAD l) result)))))

(define zip
  (lambda (i l)
    (define z
      (lambda (i l result)
        (if (ISEMPTY i)
            (reverse result '())
            (z (TAIL i) (TAIL l) (PAIR (PAIR (HEAD i) (HEAD l)) result)))))
    (z i l '())))

(zip '(1 2 3) '(4 5 6))