function Chain(){
  this.links = [];
}

Chain.prototype.link = function link(cb){
  this.links.push(cb);
  return this;
}

Chain.prototype.run = function run(end){
  var self = this;
  var next = function(i){
    return function(){
      if (i < self.links.length){
        self.links[i](next(i+1), end); // i++ makes it harder to reason about this line
      } else {
      	end() // <-- end will not be called unless the chain is explicitly ended in a link
      }
    }
  };
  next(0)();
}