rsvp.js

k" were instead called "method" or "attr". If it was `for (var method in listPromise)` it'd be much clearer what's going on, whereas single-letter variables like i, j, and k are, to me, stand-ins for integers. It was also confusing, as you said, that the function uses destructive update rather than treating the input as a value. James did mention this ("augmenting the list with promise methods"), but it's still unexpected, especially when the function is preceded by a Haskell type signature. The reason I only say I'm closer to understanding, and not quite there yet, is I'm not sure what it means to do `new Promise()` or what is being copied over in the above for-loop. I tried James's code with a Promises/A+ implementation, rsvp.js (https://github.com/tildeio/rsvp.js), but it won't let me do `new Promise()` because it works differently: > var promise = new RSVP.Promise(); TypeError: You must pass a resolver function as the sole argument to the promise constructor Per an example in RSVP.js's readme, it's expecting this: var promise = new RSVP.Promise(function(resolve, reject){ // set up a callback that calls either resolve(...) // or reject(...) }); If James is using a specific promises implementation in his code, it appears to be the one he defined in a past blog post (http://blog.jcoglan.com/2011/03/11/promises-are-the-monad-of...), which in turn builds on a module from his JS.Class library (http://jsclass.jcoglan.com/deferrable.html), which I hadn't heard of before. I still think this is a great article, but that code snippet has proven to be quite a puzzle.

tildeio/rsvp.js 2: https://github.com/promises-aplus/promises-spec 3: https://news.ycombinator.com/item?id=4661620