PromiseKit callback chaining

promiseKitExample.m

// Method signatures

// Promise resolves to User instance
- (PMKPromise *)loginToRemoteServer:(NSString *)userId; 

// Promise resolves to NSDictionary of user data
- (PMKPromise *)retrieveUserData:(User *)user; 

// Promise resolves to UIImage
- (PMKPromise *)retrieveProfileImage:(NSURL *)imageURL; 
[self loginToRemoteServer:userId].then(^(User *user) {
    self.user = user;
    [self retrieveUserData:user].then(^(NSDictionary *userData){
         self.user.data = userData;
         [self retrieveProfileImage:userData.profileImageURL].then(^(UIIMage *userImage){
               self.user.profileImage = userImage;
         });
    });
})