Task

Create a stack-based evaluator for an expression in   reverse Polish notation (RPN)   that also shows the changes in the stack as each individual token is processed as a table.



 Assume an input of a correct, space separated, string of tokens of an RPN expression
 Test with the RPN expression generated from the   Parsing/Shunting-yard algorithm   task: 

         3 4 2 * 1 5 - 2 3 ^ ^ / + 

 Print or display the output here


Notes

    ^    means exponentiation in the expression above.
    /    means division.


See also

   Parsing/Shunting-yard algorithm for a method of generating an RPN from an infix expression.
   Several solutions to 24 game/Solve make use of RPN evaluators (although tracing how they work is not a part of that task).
   Parsing/RPN to infix conversion.
   Arithmetic evaluation.


 
grammar rpnC ;
//
//  rpn Calculator
//
//  Nigel Galloway - April 7th., 2012
//
@members {
Stack<Double> s = new Stack<Double>();
}
rpn	:	(WS* (num|op) (WS | WS* NEWLINE {System.out.println(s.pop());}))*;
num	:	'-'? Digit+ ('.' Digit+)? {s.push(Double.parseDouble($num.text));};
Digit	:	'0'..'9';
op	:	'-' {double x = s.pop(); s.push(s.pop() - x);}
	|	'/' {double x = s.pop(); s.push(s.pop() / x);}
	|	'*' {s.push(s.pop() * s.pop());}
	|	'^' {double x = s.pop(); s.push(Math.pow(s.pop(), x));}
	|	'+' {s.push(s.pop() + s.pop());};
WS	:	(' ' | '\t'){skip()};
NEWLINE	:	'\r'? '\n';
 