RBPromise *promise = [RBPromise new];

promise.then(^id(NSString *result) {
  // execute any code when succeeded
  NSLog(@"success with result %@", result);

  return result;

}, ^id(NSException *exception) {
  // handle any exception
  NSLog(@"failed with exception %@", result);

  return exception;
});

[promise.resolve:@"hello world"]; // Rebelle will automatically call your success or exception callbacks

@implementation WebService

- (RBPromise *)getUser(int id) {
  self.promise = [RBPromise new];

  NSURLRequest aRequest = // request to server;

  // Call the server and get data about user
  // If you use classes that use delegates instead of callbacks, then you'll need
  // to save your promise inside a class attribute, otherwise just call it inside your blocks

  NSURLConnection *connection = [NSURLConnection connectionWithRequest:aRequest delegate:self];

  // this promise result (when succeeded) should be a User object
  return self.promise; // Return your promise so you can add chain blocks on it !
}

- (RBPromise *)getTweets:(User *)user {
  // Same idea than in getUser
  // This promise result is an NSArray of Tweet objects
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
  [self.promise resolve: // result from the response];
}

@end

@implementation  MyApp

- (RBPromise *)sample {
  WebService *ws = [WebService new];

  // you 
  RBPromise *promise = [ws getUser];

  promise.then(^id(User *user) { user.lastLoggedIn = new Date(); return user; }, nil)
         .then(^id(User *user) { return [ws getTweets:user]; }, nil);
         .then(^id(NSArray *tweets) { // This code is executed only when tweets have been downloaded }, nil);

  return promise; // You can either return once again your promise so that any upper code chain on it too...
  // Everyhing will be resolved in the order when previous code has been executed !
}

@end