2.23.scm

;;;; 2.23
;; The procedure `for-each` is similar to map. It takes as arguments a procedure and a list of elements. However, rather than forming a list of the results, `for-each` just applies the procedure to each of the elements in turn, from left to right. The values returned by applying the procedure to the elements are not used at all -- `for-each` is used with procedures that perform an action, such as printing. For example,
;;
;; (for-each (lambda (x) (newline) (display x))
;;           (list 57 321 88))
;; 57
;; 321
;; 88
;;
;; The value returned by the call to for-each (not illustrated above) can be something arbitrary, such as true. Give an implementation of for-each.

;;; Answer
(define (for-each func items)
  (func (car items))
  (if (not (null? (cdr items)))
    (for-each func (cdr items))))

;; Test
(for-each (lambda (x) (display x) (newline))
          (list 57 321 88))