Resolvable generators

example.php

<?php

// this is our generator, dns\* and socket\* are assumed
// to be async functions returning promises
function read_data_from($hostname, $port) {
  $ip = yield dns\resolve($hostname);
  $socket = yield socket\connect($ip, $port);
  
  echo yield socket\read(1024);
};

// Let's schedule it
//
// Maybe we can also change the event-loop to automatically 
// try to resolve Generators in the tick handlers
$loop->nextTick(function() {
    React\Promise\resolve(read_data_from('google.com', 80));
});

resolve.php

<?php

// Changes to React\Promise\resolve
// They probably should be pushed to a separate function

function resolve($promiseOrValue = null)
{
    // a generator is resolved when the iterator is invalid
    // then it can be used like a normal value (FullfilledPromise)
    if ($promiseOrValue instanceof \Generator && $promiseOrValue->valid()) {
        $deferred = new Deferred();

        // resolve value the generator is waiting for
        resolve($promiseOrValue->current())->then(
            function ($result) use ($promiseOrValue, $deferred) {
                // resume generator
                $promiseOrValue->send($result);

                // try to resolve generator
                resolve($promiseOrValue)->then(function () use ($deferred) {
                    $deferred->resolve();
                });
            }
        );

        return $deferred->promise();
    }

    if (!$promiseOrValue instanceof PromiseInterface) {
        return new FulfilledPromise($promiseOrValue);
    }

    if ($promiseOrValue instanceof ExtendedPromiseInterface) {
        return $promiseOrValue;
    }

    return new Promise(function ($resolve, $reject, $notify) use ($promiseOrValue) {
        $promiseOrValue->then($resolve, $reject, $notify);
    });
}

test.php

<?php

// working example - contained to React\Promise

require_once "vendor/autoload.php";

use React\Promise\Deferred;
use React\Promise;

$d = [new Deferred(), new Deferred(), new Deferred()];
$p = array_map(function ($v) { return $v->promise(); }, $d);


function make_generator(array $work)
{
    for ($i=0; $i<count($work); $i++) {
        echo $i . ": " . (yield $work[$i]) . "\n";
    }
}


$gen = make_generator(array_merge($p, ["not-a-promise"]));
Promise\resolve($gen)->then(function() {
    echo "end\n";
});

echo "start\n";

$d[0]->resolve("p1 resolved");
$d[1]->resolve("p2 resolved");
$d[2]->resolve("p3 resolved");