source: branches/f4grobner/priority-queue.lisp

;;; -*-  Mode: Lisp -*- 
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;;;  Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>          
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;;;  This program is free software; you can redistribute it and/or modify        
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(defpackage "PRIORITY-QUEUE"
  (:use :cl :heap)
  (:export "PRIORITY-QUEUE"
           "PRIORITY-QUEUE-ELEMENT-TYPE"
           "PRIORITY-QUEUE-TEST"
           "ENQUEUE"
           "DEQUEUE"
           "QUEUE-EMPTY-P"
           "QUEUE-SIZE"
           )
  (:documentation "Implements a priority queue."))

(in-package :priority-queue)

(defclass priority-queue ()
  ((element-type :initarg :element-type 
                 :initform 'fixnum 
                 :accessor priority-queue-element-type 
                 :type symbol
                 :documentation "Element type stored in this queue.")
   (test :initarg :test 
         :accessor priority-queue-test
         :documentation "The partial order used in element comparison.")
   (heap :documentation "A private slot holding the heap."))
  (:documentation "Represents a priority queue based on heaps.  Slots
HEAP and TEST are read-only after they are initialized. The slot
ELEMENT-TYPE can be overriden in subclasses, by initializing it in
a :BEFORE or an :AFTER method."))


(defmethod initialize-instance :around ((self priority-queue) 
                                       &key 
                                         (test #'<=)
                                         (element-key #'identity))
  "Fill in the HEAP slot with an instance of a heap. NOTE: This has to
be an :AROUND method, so that the slot ELEMENT-TYPE can be initialized
in a :BEFORE or :AFTER method of a subclass of PRIORITY-QUEUE."
  (with-slots (heap (test-x test) element-type)
      (call-next-method)
    (setf heap (make-heap :element-type element-type)
          test-x #'(lambda (x y) 
                     (funcall test 
                              (funcall element-key y) 
                              (funcall element-key x)))))
  self)
  
(defgeneric enqueue (self item)
  (:method ((self priority-queue) (item t))
    (with-slots (heap test)
        self
      (heap-insert heap item test))
    self))

(defgeneric dequeue (self)
  (:method ((self priority-queue))
    (with-slots (heap test)
        self
      (heap-remove heap test))))

(defgeneric queue-empty-p (self)
  (:method ((self priority-queue))
    (with-slots (heap)
        self
      (heap-empty-p heap))))

(defgeneric queue-size (self)
  (:method ((self priority-queue))
    (with-slots (heap)
        self
    (heap-size heap))))