Emacs Lisp for loop macro

for-loop.el

(defmacro for (loopvar in listvar &rest body)
  "Execute a simple for loop: (for x in '(1 2 5) (print x))."

  ;; syntax checking
  (if (symbolp loopvar) t
    (error (format "Syntax error 'for %s<- ...': LOOPVAR has to be a symbol" loopvar)))
  (if (equal (symbol-name in) "in") t
    (error (format "Syntax error 'for %s %s<- ...'" loopvar (symbol-name in))))

  ;; unintered symbols for local variables
  (let ((iterator (make-symbol "i"))
	(end (make-symbol "end"))
	(res (make-symbol "res")))

    ;; implementation
    `(if (not (listp ,listvar))
	 (error (format "Wrong type of argument for LISTVAR: %s" ,listvar))
       (let ((items ,listvar)
	     (,iterator 0)
	     (,end (length ,listvar))
	     (,res))
	 (while (< ,iterator ,end)
	   (setq ,loopvar (nth ,iterator items))
	   (setq ,res ,@body)
	   (setq ,iterator (+ 1 ,iterator))
	   )
	 ,res))))

(defun push-append (newelt place)
  (setcdr (last place) (cons newelt nil))
  place)

(defun range (end &optional start step reverse)
  ;; defaults
  (or start (setq start 0))
  (or step (setq step 1))

  (let ((i start) (res (list start)))
    (while (< i end)
      (setq i (+ i step))
      (if reverse
	  (push i res)
	(push-append i res)))
    res))

(defun sum (&rest items)
  (let ((res 0))
    (for x in items
	 (setq res (+ res x)))))

(defun ! (n)
  "Factorial calculation for N"
  (if (and (numberp n) (>= n 0))
      (if (eq n 0) (setq n 1))
    (error "N has to be a non-negative integer"))
  (apply '* (range n 1)))

;; examples
(range 5 1 2 t)          ; => (5 3 1)
(apply 'sum (range 10))  ; => 55
(! 4)                    ; => 24