[usernameqwerty004]

Look at this example code from [Amphp](https://amphp.org/):

try {
$request = new Request(“https://amphp.org/”);
$response = yield $http->request($request); // Yield a promise

if ($response->getStatus() !== 200) {
throw new HttpException;
}
} catch (HttpException $e) {
// handle error
}

This code-snippet is pure, no IO is happening. If the request call had been written as

$response = $http->request($request);

it would have been effectful, not pure; we’d have to mock the $http object when testing it. Using `yield`, we don’t. Does this mean we can remove the need for mocks if we use generators and wrap all side-effects in promises, as Amphp does? Discuss in small groups. 🙂

The “imperative shell” in this scenario is the event loop resolving the promises. All other code can be pure.

A bonus is that we also get non-blocking IO (concurrency) this way.

(Resources about functional core, imperative shell can be found [here](https://gist.github.com/kbilsted/abdc017858cad68c3e7926b03646554e)).

[Jake_Jeremy]

I don’t get why this for you means that you wouldn’t have to mock `$http` during testing, or why this isn’t a side effect in your eyes.

[MorphineAdministered]

I’m not sure what IO testing you have in mind. This code fragment doesn’t contain any IO, and the fact that it uses generator has nothing to do with it – it just doesn’t.

To test “no-yield” version of this code you would pass `$http` stub that returns `$fakeResponse` you want to test your code with, and here you need to pass fake `$http` (that yields some `Promise` dummy) and then send `$fakeResponse` to generator – that’s the only difference.

[HenkPoley]

Tangentially related, maybe you’ll like Phel: https://phel-lang.org/#why-phel

But from a cursory look, there are many other attempts.

[__matta]

I get that you can send data into generators instead of yielding their value, and that you could use that to send in a test response, but I’m not sure how you would get a handle on the generator in your test to call send.

Are you counting on the global event loop to provide a way for you to get the promise?

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