Promise.cast and Promise.resolve

Kevin Smith zenparsing at
Wed Jan 29 07:33:01 PST 2014

> It is, actually, more simplicity. The concept of `Promise.resolve` and
> `Promise.chain` is simpler than `Promise.cast` and `Promise.then` (i.e.:
> they represent orthogonal concepts, not "complected"). `Promise.cast` and
> `Promise.then` may be, arguably, *easier* to work with, from a user POV,
> since you don't need to make as many choices. I would argue that it would
> make more sense to write `cast` and `then` in terms of `resolve` and
> `chain`, however. But this seems to have already been decided.

It does make more sense, and from my point of view it's not decided.  What
is decided is the AP2 design.  That is:

1)  promises are fully parametric and,
2)  `then` recursively unwraps the *input* to its callbacks.

For the sake of coherency (aka conceptual integrity), `then` needs to be
written in terms of `chain`.  This issue needs to be resolved ASAP,
however, since promises are making their way into engines now.
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