tasks a-s

Task/Parsing-RPN-calculator-algorithm/Icon/parsing-rpn-calculator-algorithm.icon

@@ -0,0 +1,33 @@
+procedure main()
+   EvalRPN("3 4 2 * 1 5 - 2 3 ^ ^ / +")
+end
+
+link printf
+invocable all
+
+procedure EvalRPN(expr)          #: evaluate (and trace stack) an RPN string
+
+   stack := []
+   expr ? until pos(0) do {
+      tab(many(' '))                         # consume previous seperator
+      token := tab(upto(' ')|0)              # get token
+      if token := numeric(token) then {      # ... numeric
+         push(stack,token)
+         printf("pushed numeric   %i : %s\n",token,list2string(stack))
+         }
+      else {                                 # ... operator
+         every b|a := pop(stack)             # pop & reverse operands
+         case token of {
+            "+"|"-"|"*"|"^"   : push(stack,token(a,b))
+            "/"               : push(stack,token(real(a),b))
+            default           : runerr(205,token)
+            }
+         printf("applied operator %s : %s\n",token,list2string(stack))
+         }
+   }
+end
+
+procedure list2string(L)         #: format list as a string
+   every (s := "[ ") ||:= !L || " "
+   return s || "]"
+end