<?php
namespace Sabre\Event;
use Generator;
use Exception;
/**
* Turn asynchronous promise-based code into something that looks synchronous
* again, through the use of generators.
*
* Example without coroutines:
*
* $promise = $httpClient->request('GET', '/foo');
* $promise->then(function($value) {
*
* return $httpClient->request('DELETE','/foo');
*
* })->then(function($value) {
*
* return $httpClient->request('PUT', '/foo');
*
* })->error(function($reason) {
*
* echo "Failed because: $reason\n";
*
* });
*
* Example with coroutines:
*
* coroutine(function() {
*
* try {
* yield $httpClient->request('GET', '/foo');
* yield $httpClient->request('DELETE', /foo');
* yield $httpClient->request('PUT', '/foo');
* } catch(\Exception $reason) {
* echo "Failed because: $reason\n";
* }
*
* });
*
* @copyright Copyright (C) 2013-2015 fruux GmbH. All rights reserved.
* @author Evert Pot (http://evertpot.com/)
* @license http://sabre.io/license/ Modified BSD License
*/
function coroutine(callable $gen) {
$generator = $gen();
if (!$generator instanceof Generator) {
throw new \InvalidArgumentException('You must pass a generator function');
}
// This is the value we're returning.
$promise = new Promise();
$lastYieldResult = null;
/**
* So tempted to use the mythical y-combinator here, but it's not needed in
* PHP.
*/
$advanceGenerator = function() use (&$advanceGenerator, $generator, $promise, &$lastYieldResult) {
while ($generator->valid()) {
$yieldedValue = $generator->current();
if ($yieldedValue instanceof Promise) {
$yieldedValue->then(
function($value) use ($generator, &$advanceGenerator, &$lastYieldResult) {
$lastYieldResult = $value;
$generator->send($value);
$advanceGenerator();
},
function($reason) use ($generator, $advanceGenerator) {
if ($reason instanceof Exception) {
$generator->throw($reason);
} elseif (is_scalar($reason)) {
$generator->throw(new Exception($reason));
} else {
$type = is_object($reason) ? get_class($reason) : gettype($reason);
$generator->throw(new Exception('Promise was rejected with reason of type: ' . $type));
}
$advanceGenerator();
}
)->error(function($reason) use ($promise) {
// This error handler would be called, if something in the
// generator throws an exception, and it's not caught
// locally.
$promise->reject($reason);
});
// We need to break out of the loop, because $advanceGenerator
// will be called asynchronously when the promise has a result.
break;
} else {
// If the value was not a promise, we'll just let it pass through.
$lastYieldResult = $yieldedValue;
$generator->send($yieldedValue);
}
}
// If the generator is at the end, and we didn't run into an exception,
// we can fullfill the promise with the last thing that was yielded to
// us.
if (!$generator->valid() && $promise->state === Promise::PENDING) {
$promise->fulfill($lastYieldResult);
}
};
try {
$advanceGenerator();
} catch (Exception $e) {
$promise->reject($e);
}
return $promise;
}
