deletion endpoint, newest endpoint, queue implementation

1 files changed, 40 insertions, 0 deletions

diff --git a/src/util.lisp b/src/util.lisp
index 2fc079b..ad312eb 100644
--- a/src/util.lisp
+++ b/src/util.lisp
@@ -18,3 +18,43 @@
                                              :key #'symbol-name)))
          ,@body))))
 
+
+(defclass queue-buffer ()
+  ((front :initform (list))  
+   (back :initform (list))   
+   (size :initform 0)
+   (capacity :initarg capacity)))
+
+(defun make-qb (capacity)
+  (make-instance 'queue-buffer :capacity capacity))
+
+(defun qb-empty-p (q)
+  (zerop (slot-value q 'size)))
+
+(defun qb-full-p (q)
+  (= (slot-value q 'size) (slot-value q 'capacity)))
+
+(defun enqueue-qb (q x)
+  (when (qb-full-p q) (dequeue-qb q))
+  (with-slots (size back) q
+    (push x back)
+    (incf size)))
+
+(defun dequeue-qb (q &optional default)
+  (with-slots (front back size) q
+    (cond
+      ((plusp size) 
+       (when (null front)
+         (setf front (nreverse back)
+               back nil))
+       (decf size)
+       (pop front))
+
+      (t  default))))
+
+(defun qb-look (q)
+  "get a list of the queue, but don't remove items from it"
+  (with-slots (front back) q
+    (nconc (copy-seq front)
+           (reverse back))))
+