/ 
Evo-0.0206
River stage one • 1 direct dependent • 1 total dependent
/ Evo::Promise

NAME

Evo::Promise

VERSION

version 0.0206

FUNCTIONS

promise

promise(
  sub($resolve, $reject) {
    loop_timer 1 => sub { $resolve->('HELLO') };
  }
)->then(sub($v) { say "Fulfilled: $v"; });

Return ES6 syntax promise. The first argument should be a function. Resolve and reject handlers(functions) will be passed to it

Only the first invocation of either $resolve or $reject matters. The second one will be ignored.

deferred

Create a promise and attach it to the deferred object. Deferred object is a handler for the promise.

my $d = deferred();
loop_timer 1 => sub { $d->resolve('HELLO') };
$d->promise->then(sub($v) { say "Fulfilled: $v"; });

promise_resolve

my $p = promise_resolve('hello');

Generate a resolved promise with a given value. If value is a thenable object or another promise, the resulting promise will follow it. Otherwise it will be fulfilled with that value

promise_reject

my $p = promise_reject('hello');

Generate a rejected promise with a reason. If the reason is a promise, resulting promise will NOT follow it.

promise_all

Creates a promise that will be resolved only when all promise are resolved. The result will be an array containing resolved value with the same order, as passed to this function. If one of the collected promise become rejected, that promise will be rejected to with that reason.

my ($d1, $d2) = (deferred, deferred);
loop_timer 1,   sub { $d1->resolve('first') };
loop_timer 0.1, sub { $d2->resolve('second') };

promise_all($d1->promise, $d2->promise)->then(sub($v) { say join ';', $v->@* });

Will print first;second

"spread" will help a lot

promise_race

Return a promise that will be resolved or rejected with the value/reason of the first resolved/rejected promise

promise_race($d1->promise, $d1->promise)->then(sub($v) { say $v });

loop_timer 1 => sub { $d1->resolve('1') };
loop_timer 2 => sub { $d2->resolve('2') };

Will print 2

METHODS

then

Make a chain and return a promise. The 2 args form onResolve, onReject isn't recommended. Better use "catch"

$promise->then(sub($v) { say "Resolved $v" })->then(sub($v) { say "Step 2 $v" });
$promise->then(sub($v) { say "Resolved $v" }, sub($r) { say "Rejected $r" });

catch

The same as then(undef, sub($r) {}), recommended form

$d->promise->then(sub { })->catch(sub($r) { say "Rejected with $r" });

spread

If you expect promise gets fulfilled with the array reference, you can dereference it and pass to function

promise_all(first => $d1->promise, second => $d2->promise) ->spread(sub(%res) { say $_ , ': ', $res{$_} for keys %res });

fin

Chain promise with a handler, that gets called with no argument when the parent promise is settled(fulfilled or rejected). When that handler returns a result, the next promise gets postponed. Value are ignored. If that handler causes an exception or returns rejected promise (or promise that will eventually gets rejected), the chain would be rejected.

A shorter. Causes no effect on the chain unless rejection happens

promise_resolve('VAL')->fin(sub() {'IGNORED'})->then(sub($v) { say $v});

Usefull for closing connections etc. The idea described here: https://github.com/kriskowal/q#propagation

IMPLEMENTATION

This is a sexy and fast non-recursive implementation of Promise/A+

The end-user library Evo::Promise works with Evo::Loop (promise require event loop because of https://promisesaplus.com/#point-34) But the main part (see Evo::Promise::Driver) is designed to be reused and it's ridiculously simple to implement variant for other loops with a few lines of code (see the source code of Evo::Promise)

Different implementations of promise should work together well by design. Right now there are other implementations in CPAN. But when I tested them(2016yr), they were far away from A+ and contained many bugs. So if need to mix different promise libraries, try to start the chain from this one

SEE ALSO

More info about promise, race, all etc.: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Promise

AUTHOR

alexbyk.com

COPYRIGHT AND LICENSE

This software is copyright (c) 2016 by alexbyk.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.