March 2014 update

Task/Parsing-RPN-calculator-algorithm/Common-Lisp/parsing-rpn-calculator-algorithm.lisp

@@ -0,0 +1,20 @@
+(setf (symbol-function '^) #'expt)  ; Make ^ an alias for EXPT
+
+(defun print-stack (token stack)
+    (format T "~a: ~{~a ~}~%" token (reverse stack)))
+
+(defun rpn (tokens &key stack verbose )
+  (cond
+    ((and (not tokens) (not stack)) 0)
+    ((not tokens) (car stack))
+    (T
+      (let* ((current (car tokens))
+             (next-stack (if (numberp current)
+                           (cons current stack)
+                           (let* ((arg2 (car stack))
+                                  (arg1 (cadr stack))
+                                  (fun (car tokens)))
+                             (cons (funcall fun arg1 arg2) (cddr stack))))))
+        (when verbose
+          (print-stack current next-stack))
+        (rpn (cdr tokens) :stack next-stack :verbose verbose)))))