Code sample taken from http://www.techsfo.com/blog/2013/08/managing-nested-asynchronous-callbacks-in-objective-c-using-reactive-cocoa/. signalGetNetworkStep makes an async call to an endpoint.

gistfile1.txt

__weak id weakSelf = self;
[[[[[self signalGetNetworkStep1] flattenMap:^RACStream*(id *x) {
   // perform your custom business logic
   return [weakSelf signalGetNetworkStep2:x];
}] flattenMap:^RACStream*(id *y) {
   // perform additional business logic
   return [weakSelf signalGetNetworkStep3:y];
}] flattenMap:^RACStream*(id *z) {
   // more business logic
   return [weakSelf signalGetNetworkStep4:z];
}] subscribeNext:^(id*w) {
   // last business logic
}];