June 2018 Update

Task/Priority-queue/XLISP/priority-queue-1.xlisp

@@ -0,0 +1,35 @@
+(define-class priority-queue
+	(instance-variables queue lowest-priority most-urgent) )
+
+(define-method (priority-queue 'initialize limit)
+	(defun setup (x)
+		(vector-set! queue x nil)
+		(if (< x limit)
+			(setup (+ x 1)) ) )
+	(setq lowest-priority limit)
+	(setq most-urgent limit)
+	(setq queue (make-vector (+ limit 1)))
+	(setup 0)
+	self )
+
+(define-method (priority-queue 'push item priority)
+	(if (and (integerp priority) (>= priority 0) (<= priority lowest-priority))
+		(progn
+			(setq most-urgent (min priority most-urgent))
+			(vector-set! queue priority (nconc (vector-ref queue priority) (cons item nil))) ) ) )
+
+(define-method (priority-queue 'pop)
+	(defun find-next (q)
+		(if (or (= q lowest-priority) (not (null (vector-ref queue q))))
+			q
+			(find-next (+ q 1)) ) )
+	(define item (car (vector-ref queue most-urgent)))
+	(vector-set! queue most-urgent (cdr (vector-ref queue most-urgent)))
+	(setq most-urgent (find-next most-urgent))
+	item )
+
+(define-method (priority-queue 'peek)
+	(car (vector-ref queue most-urgent)) )
+
+(define-method (priority-queue 'emptyp)
+	(and (= most-urgent lowest-priority) (null (vector-ref queue most-urgent))) )