Another update from ingydotnet^djgoku

Task/Priority-queue/Common-Lisp/priority-queue.lisp

@@ -0,0 +1,32 @@
+;priority-queue's are implemented with association lists
+(defun make-pq (alist)
+  (sort (copy-alist alist) (lambda (a b) (< (car a) (car b)))))
+;
+;Will change the state of pq
+;
+(define-modify-macro insert-pq (pair)
+                     (lambda (pq pair) (sort-alist (cons pair pq))))
+
+(define-modify-macro remove-pq-aux () cdr)
+
+(defmacro remove-pq (pq)
+  `(let ((aux (copy-alist ,pq)))
+     (REMOVE-PQ-AUX ,pq)
+     (car aux)))
+;
+;Will not change the state of pq
+;
+(defun insert-pq-non-destructive (pair pq)
+  (sort-alist (cons pair pq)))
+
+(defun remove-pq-non-destructive (pq)
+  (cdr pq))
+;testing
+(defparameter a (make-pq '((1 . "Solve RC tasks") (3 . "Clear drains") (2 . "Tax return") (5 . "Make tea"))))
+(format t "~a~&" a)
+(insert-pq a '(4 . "Feed cat"))
+(format t "~a~&" a)
+(format t "~a~&" (remove-pq a))
+(format t "~a~&" a)
+(format t "~a~&" (remove-pq a))
+(format t "~a~&" a)