Reverse Polish Notation Calculator

reverse_polish.js

function calc(expr) {
  return expr.split(/\s+/).reduce(function(stack, current){
    var a, b, c;
    if(/[+\-*\/]/.test(current)){
      b = stack.pop();
      a = stack.pop();
      switch(current) {
        case '+': c = a + b; break;
        case '-': c = a - b; break;
        case '*': c = a * b; break;
        case '/': c = a / b; break;
      }
    } else {
      c = parseFloat(current);
    }
    stack.push(c);
    return stack;
  }, []).pop() || 0; // readability: low, fun: high
}