ex_2_23.clj

(ns sicp.chapter-2.part-2.ex-2-23
  (:require
    [sicp.misc :as m]))

; Exercise 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.

(defn for-each
  [proc items]
  (if (m/list-empty? items)
    true
    (do
      (proc (m/car items))
      (for-each proc (m/cdr items)))))

(comment
  (for-each #(println %) (list 57 321 88)))