function tco(f) {
  var value;
  var active = false;
  var accumulated = [];
  return function accumulator() {
    accumulated.push(arguments);
    if(!active) {
      active = true;
      while(accumulated.length) {
        value = f.apply(this, accumulated.shift());
      }
      active = false;
      return value;
    }
  };
}
var sum = tco(function(x, y) {
  if(y > 0) {
    return sum(x + 1, y - 1);
  } else {
    return x;
  }
});
let res = sum(1, 5)
console.info(res);