loop-macro.lisp

;; Fun with macros and loops
;; Implementation of a C-like for loop facility

(defmacro for-continue ()
  `(go loop-continue))

(defmacro for-break ()
  `(go loop-break))

(defmacro for-loop ((&rest initializations) condition (&rest iterations)
		    &body operations)
  `(block nil
     (let ,(loop for n in initializations collect `(,@n))
       (tagbody
	loop
	  (if (not ,condition)
	      (go loop-break))
	  (progn ,@operations)
	loop-continue
	  (progn ,@iterations)
	  (go loop)
	loop-break))))


;; Iterating integer
(for-loop ((i 0)) (< i 10) ((incf i))
  (print i))

;; Iterating over a list
(for-loop ((n (list 1 2 3))) (not (null n)) ((setf n (rest n)))
  (print (first n)))

;; Iterating over both a list repeatedly and an integer limit
(defvar *l*)
(setf *l* (list 1 2 3))
(for-loop ((i 0) (n *l*))
    (< i 256)
    ((incf i) (setf n (rest n)))
  (if (null (first n))
      (setf n *l*))
  (print (list i (first n))))