Author: abaine Date: Mon Jul 2 18:39:22 2007 New Revision: 37

Added: trunk/funds/src/stack/ trunk/funds/src/stack/stack.lisp Log: Initial version of stack.

Added: trunk/funds/src/stack/stack.lisp ============================================================================== --- (empty file) +++ trunk/funds/src/stack/stack.lisp Mon Jul 2 18:39:22 2007 @@ -0,0 +1,30 @@ + +(in-package :funds) + +(defun make-stack () + "An empty stack." + nil) + +(defun stack-push (item stack) + "The stack that results when the given item is pushed onto the given stack." + (cons item stack)) + +(defun stack-pop (stack) + "The stack that results when the top item is popped off the given stack." + (cdr stack)) + +(defun stack-top (stack) + "The top item on the given stack." + (car stack)) + +(defun stack-empty-p (stack) + "Whether the given stack is empty." + (null stack)) + +(defun stack-length (stack) + "The number of items on this stack; note that this is an O(n) operation." + (labels ((f (stack accum) + (if (stack-empty-p stack) + accum + (f (stack-pop stack) (1+ accum))))) + (f stack 0)))