An imperative implementation of map in scheme

map.scm

#lang r5rs

;Scheme doesn't come with a while loop so we create our own.
(define-syntax while 
  (syntax-rules (while-loop)
    ((while cond stmt1 stmt2 ...) 
     (letrec ((while-loop 
               (lambda () 
                 (if cond 
                     (begin stmt1 stmt2 ... (while-loop)) 
                     '())))) 
       (while-loop)))))

;Test if to values are not equal
(define (neqv? a b) (not (eqv? a b)))

;Construct a new list by applying a function on each element
;of the original list.
(define 
  (map f l)
  (let* ((nl (cons '() l))
         (p nl))
  (while (neqv? l '())
   (set-cdr! p (cons (f (car l)) (cdr l)))
   (set! p (cdr p))
   (set! l (cdr l)))
  (cdr nl)))
	
;Display the squares of the numbers 1 to 10
(display (map
 (lambda (x) (* x x))
 (list 1 2 3 4 5 6 7 8 9 10)))