Reverse zip

rzip.rkt

#lang racket

;; Inspired by SICP, chapter 5.2.2, and
;; https://www.youtube.com/watch?v=SrKj4hYic5A

(define (rzip c1 c2)
  (let iter ([a c1] [z c2] [receive (λ (x y) y)])
    (if (null? a)
        (receive z '())
        (iter (cdr a) z
              (λ (y acc)
                (receive (cdr y)
                         (cons (cons (car a) (car y))
                               acc)))))))

(module+ test
  (require rackunit)
  (check-equal? (rzip '(a b c) '(1 2 3))
                '((a . 3) (b . 2) (c . 1))))