Well done on making a whole language though. It's pretty challenging and I hope you do well.
Aside: This seems very similar to narrativeJS in concept http://www.neilmix.com/narrativejs/doc/
*jQuery or promises like API object, whereupon you place methods- some of which may be asynchronous. an asynchronous operation returns an object with a method that performs the next action and optionally takes a callback, passing in the results of the previous asynchronous operation as a value- thus flattening the callbacks out into a sequence instead of a nesting.
Constructed properly, you can create monad combinators/transformers, to do things like automatically wrap every step in your chain with exception handling. Using common JS promises libraries gives you error handling for free.
as for defining "join", help me understand. How is jquery "add" not essentially that? And why pick the fmap,join formulation instead of the bind,return formulation of a monad?
The reason I picked join is because (in my view, anyway) it's the easiest demonstration of how jQuery is not a monad. There's no way to even get something of type M (M a) in jQuery, because the jQuery lifting operation is idempotent. The same exact problem exists with return, but I've found that people have a hard time seeing it with that example.
The problem I have with you referring to jQuery as a monad, even by analogy, is that jQuery really really isn't a monad. It's only very loosely analogous, and that analogy is more likely to teach people the wrong things about monads rather than the right ones.
For the case in hand though, you can get to almost but not quite really technically a monad, and still cure most of the nested callback headaches. One way I think about monads is they are a strategy for turning nested functions into sequentially composed functions. Which is, pretty much what we want, right?
More to the point, I don't understand why we (HN and the JS community at large) keep having this discussion. Coroutines have been around since the 60s. This is a solved problem.