[lmeyerov]

Promises are single assignment, so they solve the problem. As soon as they resolve, they're safe. Calls to them don't happen until they resolve. If you want to change the logger, you use streams, which will handle safe replacement for you (flatmap).

We do some crazy async HPC code, and during on-boarding, new members invariably get some initialization / error handling wrong with raw callbacks, and convert pretty quick to FRP after that. Unstructured async is crazy.

[dalke]

Yes, the example problem doesn't match to promises.

I don't understand the "change the logger" comment. The example was the logger sends a message to the listener, which opens a database handle, which sends a message to the logger, and repeat. There's nothing to changing. I don't see how FRP helps eliminate that cycle.

[lmeyerov]

This might be what's happening, which would surface as no sensible declaration ordering:

//try making the logger first

var logger = require('myLogger')(backends);

var listener1 = require('mySync')(logger);

var backends = Rx.Observable.fromArray([listener1, listener2]);

//try making the backends first

var listener1 = require('mySync')(logger);

var backends = Rx.Observable.fromArray([listener1, listener2]);

var logger = require('myLogger')(backends);

From there, you'd switch to unsafe FRP methods (imperatively injecting into event streams, e.g., Subjects in Rx), which is the warning sign of weird cyclic behavior.