yielding.lisp

yielding.lisp

(defmacro yielding (&body body)
  (let ((gtail (gensym))
	(ghead (gensym))
	(garg (gensym))
	(gtmp (gensym)))
    `(let* ((,ghead (cons nil nil))
	    (,gtail ,ghead))
       (macrolet
	   ((yield (,garg) `(setf (cdr ,',gtail) (cons ,,garg nil)
				  ,',gtail (cdr ,',gtail)))
	    (yield! (,garg) `(loop :for ,',gtmp :in ,,garg :do (yield ,',gtmp))))
	 ,@body
	 (cdr ,ghead)))))