ReactiveCocoa Chaining Example

gistfile1.m

RACSignal *intervalSignal = [RACSignal interval:1];
RACSignal *startedIntervalSignal = [intervalSignal startWith:[NSDate date]];
RACSignal *mappedIntervalSignal = [startedIntervalSignal map:^id(NSDate *value) {
    NSDateComponents *dateComponents = [[NSCalendar currentCalendar] components:NSMinuteCalendarUnit | NSSecondCalendarUnit fromDate:value];
    
    return [NSString stringWithFormat:@"%d:%02d", dateComponents.minute, dateComponents.second];
}];

RAC(self.textField.text) = mappedIntervalSignal;