Why not task.js, instead?
1. Implementation complexity
let-from: trivial syntax transformation
task.js+generators: non-trivial syntax transformation or
-more likely- non-trivial runtime system manipulation
2. Usage complexity
let-from: just another statement in the block,
merely syntax for conventional promise/callback-style
task.js+generators: spawn+function*+yield,
complex rts + complex library
3. Usage granularity
let-from: statement level
task.js+generators: function level
Note that the trade-offs are not entirely against task.js: because JS
has so much non-overridable surface syntax, it is useful to have the
pre-packaged functionality of generators built-in, and it is useful to
reuse that functionality for async and co-routine code, via task.js.
As long as you use it to wrap non-trivial segments of code.
But when you don't want to deal with code that uses while/for/if/..,
or if you want to build up your code patterns from smaller
components, then let-from has advantages. For let-from to fully
replace task.js and generators, JS would need library-based
control structures or overridable control-structure syntax (eg,
Haskell monads or F# computation expressions).
Claus
Different issue: do we already have a solution for a missing error handler causing silent
failures? task.js should cover this, too (right?)
[[[Sent from a mobile device. Please forgive brevity and typos.]]]
Dr. Axel Rauschmayer
a...@rauschma.de
Home: http://rauschma.de
Blog: http://2ality.com
On 07.11.2012, at 00:42, "Claus Reinke" <claus.rei...@talk21.com> wrote:
I agree that promises should be standardized in Ecma-262.
Agreed. That would also offer the possibility to support promises
in syntax. In ES7 (latest), I would like to see something roughly like
{ ...;
let x <- promise;
...;
}
(read as "let x from promise"), desugaring into
{ ...;
promise.then( (x) => { ...; };
}
Essentially, this is an even shallower continuation than generators
(only the remaining statements in the current statement list), but it
is already sufficient to avoid callback nesting issues in async code. It also suffices to
implement generators, but for syntax.
By relying on nothing but a '.then' method, this isn't tied to promises
in the narrow sense, but provides a reusable building block for other control abstractions (to
begin with, abstracting away the default
error handling in some APIs).
Claus
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