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.


function rpn(s)
    stack = Any[]
    for op in map(eval, map(parse, split(s)))
        if isa(op, Function)
            arg2 = pop!(stack)
            arg1 = pop!(stack)
            push!(stack, op(arg1, arg2))
        else
            push!(stack, op)
        end
        println("$op: ", join(stack, ", "))
    end
    length(stack) != 1 && error("invalid RPN expression $s")
    return stack[1]
end
rpn("3 4 2 * 1 5 - 2 3 ^ ^ / +")