[B@rmaley.e><e]

var sum = function(a){
  var fnc = function(a){
    fnc.value += a || 0;
    return fnc;
  };
  fnc.value = a || 0;
  fnc.toString = toString;
  return fnc;
}, 
toString = function(){
  return this.value
};

alert(sum()); // ==> 0
alert(sum(2)); // ==> 2
alert(sum(1)(2)(3)); // ==> 6
alert(sum(4)(8)); // ==> 12
// и т.д.