Beginning of RPN calc.

rnp.rb

#!/usr/bin/env ruby

OPERATORS = {
  "x": :*,
  "/": :fdiv,
  "+": :+,
  "-": :-
}

def is_value?(token)
  true ^ OPERATORS[token.to_sym]
end


while input = gets.chomp.split
  stack = []
  input.each do |token|
    if is_value? token
      stack << token.to_i
    else
      left, right = stack.pop(2)
      val = left.send OPERATORS[token.to_sym], right
      stack << val
    end
  end
end