Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:127686
Precedence: bulk
MIME-Version: 1.0
References: <CAJpLVh3Kxk4iCWs8b3jyT7OfvxpBUbZbBo4F81Lgc7qegYT2wg@mail.gmail.com>
 <327faa47-c602-4323-a782-e2a063bd6b60@app.fastmail.com>
In-Reply-To: <327faa47-c602-4323-a782-e2a063bd6b60@app.fastmail.com>
Date: Mon, 16 Jun 2025 17:35:50 +0200
Message-ID: <CAJpLVh0RPJJoOmpkjvVhYpmAgWPw=POFE5CNRA1SXBbR5_R2fA@mail.gmail.com>
Subject: Re: [PHP-DEV] How hard would it be to add a "superyield" keyword?
To: Rob Landers <rob@bottled.codes>
Cc: internals@lists.php.net
Content-Type: multipart/alternative; boundary="00000000000049902b0637b22701"
From: olleharstedt@gmail.com (=?UTF-8?Q?Olle_H=C3=A4rstedt?=)

--00000000000049902b0637b22701
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Hi,

Great tip, thank you, I had forgot about those! Will try.

Olle

Den m=C3=A5n 16 juni 2025 kl 17:32 skrev Rob Landers <rob@bottled.codes>:

>
>
> On Mon, Jun 16, 2025, at 17:18, Olle H=C3=A4rstedt wrote:
>
> Hello Internals,
>
> I was pondering a little about effect handlers today, and how they could
> work as a replacement for dependency injection and mocking. Let me show a=
n
> example:
>
> <?php
>
> require_once("vendor/autoload.php");
>
> use Latitude\QueryBuilder\Engine\MySqlEngine;
> use Latitude\QueryBuilder\QueryFactory;
> use function Latitude\QueryBuilder\field;
>
> // Dummy db connection
> class Db
> {
>     public function getQueryBuilder()
>     {
>         return new QueryFactory(new MySqlEngine());
>     }
> }
>
> interface Effect {}
>
> class QueryEffect implements Effect
> {
>     public $query;
>
>     public function __construct($query)
>     {
>         $this->query =3D $query;
>     }
> }
>
> class Plugin
> {
>     /* The "normal" way to do testing, by injecting the db object. Not
> needed here.
>     public function __construct(Db $db)
>     {
>         $this->db =3D $db;
>     }
>     */
>
>     public function populateCreditCardData(&$receipt)
>     {
>         foreach ($receipt['items'] as &$item) {
>             // 2 =3D credit card
>             if ($item['payment_type'] =3D=3D 2) {
>                 $query =3D $this->db->getQueryBuilder()
>                     ->select('card_product_name ')
>                     ->from('card_transactions')
>                     ->where(field('id')->eq($item['card_transaction_id'])=
)
>                     ->compile();
>
>                 // Normal way: Call the injected dependency class directl=
y.
>                 //$result =3D $this->db->search($query->sql(),
> $query->params());
>
>                 // Generator way, push the side-effect up the stacktrace
> using generators.
>                 $result =3D yield new QueryEffect($query);
>                 if ($result) {
>                     $item['card_product_name'] =3D
> $result[0]['card_product_name'];
>                 }
>             }
>         }
>     }
> }
>
> // Dummy receipt
> $receipt =3D [
>     'items' =3D> [
>         [
>             'payment_type' =3D> 2
>         ]
>     ]
> ];
> $p =3D new Plugin();  // Database is not injected
> $gen =3D $p->populateCreditCardData($receipt);
> foreach ($gen as $effect) {
>     // Call $db here instead of injecting it.
>     // But now I have to propagate the $gen logic all over the call stack=
,
> with "yield from"? :(
>     // Effect handlers solve this by forcing an effect up in the stack
> trace similar to exceptions.
>
>     // Dummy db result
>     $rows =3D [
>         [
>             'card_product_name' =3D> 'KLARNA',
>         ]
>     ];
>     $gen->send($rows);
> }
>
> // Receipt item now has card_product_name populated properly.
> print_r($receipt);
>
> ---
>
> OK, so the problem with above code is that, in order for it to work, you
> have to add "yield from" from the top to the bottom of the call stack,
> polluting the code-base similar to what happens with "async" in JavaScrip=
t.
> Also see the "Which color is your function" article [1].
>
> For this design pattern to work seamlessly, there need to be a way to yie=
ld
> "all the way", so to speak, similar to what an exception does, and how
> effect handlers work in OCaml [2].
>
> The question is, would this be easy, hard, or very hard to add to the
> current PHP source code? Is it conceptually too different from generators=
?
> Would it be easier to add a way to "jump back" from a catched exception
> (kinda abusing the exception use-case, but that's how effect handlers wor=
k,
> more or less)?
>
> Thanks for reading :)
>
> Olle
>
> ---
>
> [1] -
> https://journal.stuffwithstuff.com/2015/02/01/what-color-is-your-function=
/
>
> [2] - https://ocaml.org/manual/5.3/effects.html
>
>
> You want to jump out of the current stack frame to one a higher one, and
> possibly resume execution?
>
> The best way to do that is to use fibers. They basically do exactly this
> behavior.
>
> =E2=80=94 Rob
>

--00000000000049902b0637b22701
Content-Type: text/html; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

<div dir=3D"ltr"><div>Hi,</div><div><br></div><div>Great tip, thank you, I =
had forgot about those! Will try.</div><div><br></div><div>Olle</div></div>=
<br><div class=3D"gmail_quote gmail_quote_container"><div dir=3D"ltr" class=
=3D"gmail_attr">Den m=C3=A5n 16 juni 2025 kl 17:32 skrev Rob Landers &lt;ro=
b@bottled.codes&gt;:<br></div><blockquote class=3D"gmail_quote" style=3D"ma=
rgin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:=
1ex"><u></u><div><div><br></div><div><br></div><div>On Mon, Jun 16, 2025, a=
t 17:18, Olle H=C3=A4rstedt wrote:</div><blockquote type=3D"cite" id=3D"m_2=
458363863665578536qt"><div dir=3D"ltr"><div>Hello Internals,</div><div><br>=
</div><div>I was pondering a little about effect handlers today, and how th=
ey could</div><div>work as a replacement for dependency injection and mocki=
ng. Let me show an</div><div>example:</div><div><br></div><div>&lt;?php</di=
v><div><br></div><div>require_once(&quot;vendor/autoload.php&quot;);</div><=
div><br></div><div>use Latitude\QueryBuilder\Engine\MySqlEngine;</div><div>=
use Latitude\QueryBuilder\QueryFactory;</div><div>use function Latitude\Que=
ryBuilder\field;</div><div><br></div><div>// Dummy db connection</div><div>=
class Db</div><div>{</div><div>=C2=A0 =C2=A0 public function getQueryBuilde=
r()</div><div>=C2=A0 =C2=A0 {</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 return =
new QueryFactory(new MySqlEngine());</div><div>=C2=A0 =C2=A0 }</div><div>}<=
/div><div><br></div><div>interface Effect {}</div><div><br></div><div>class=
 QueryEffect implements Effect</div><div>{</div><div>=C2=A0 =C2=A0 public $=
query;</div><div><br></div><div>=C2=A0 =C2=A0 public function __construct($=
query)</div><div>=C2=A0 =C2=A0 {</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 $thi=
s-&gt;query =3D $query;</div><div>=C2=A0 =C2=A0 }</div><div>}</div><div><br=
></div><div>class Plugin</div><div>{</div><div>=C2=A0 =C2=A0 /* The &quot;n=
ormal&quot; way to do testing, by injecting the db object. Not</div><div>ne=
eded here.</div><div>=C2=A0 =C2=A0 public function __construct(Db $db)</div=
><div>=C2=A0 =C2=A0 {</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 $this-&gt;db =
=3D $db;</div><div>=C2=A0 =C2=A0 }</div><div>=C2=A0 =C2=A0 */</div><div><br=
></div><div>=C2=A0 =C2=A0 public function populateCreditCardData(&amp;$rece=
ipt)</div><div>=C2=A0 =C2=A0 {</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 foreac=
h ($receipt[&#39;items&#39;] as &amp;$item) {</div><div>=C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 // 2 =3D credit card</div><div>=C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 if ($item[&#39;payment_type&#39;] =3D=3D 2) {</div=
><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 $query =3D $t=
his-&gt;db-&gt;getQueryBuilder()</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 -&gt;select(&#39;card_product_name &=
#39;)</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 -&gt;from(&#39;card_transactions&#39;)</div><div>=C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 -&gt;where(field(&#=
39;id&#39;)-&gt;eq($item[&#39;card_transaction_id&#39;]))</div><div>=C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 -&gt;compile=
();</div><div><br></div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 // Normal way: Call the injected dependency class directly.</div=
><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 //$result =3D=
 $this-&gt;db-&gt;search($query-&gt;sql(),</div><div>$query-&gt;params());<=
/div><div><br></div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 // Generator way, push the side-effect up the stacktrace</div><div>u=
sing generators.</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
 =C2=A0 $result =3D yield new QueryEffect($query);</div><div>=C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 if ($result) {</div><div>=C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 $item[&#39;c=
ard_product_name&#39;] =3D</div><div>$result[0][&#39;card_product_name&#39;=
];</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 }</div=
><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 }</div><div>=C2=A0 =C2=A0 =
=C2=A0 =C2=A0 }</div><div>=C2=A0 =C2=A0 }</div><div>}</div><div><br></div><=
div>// Dummy receipt</div><div>$receipt =3D [</div><div>=C2=A0 =C2=A0 &#39;=
items&#39; =3D&gt; [</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 [</div><div>=C2=
=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 &#39;payment_type&#39; =3D&gt; 2</di=
v><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 ]</div><div>=C2=A0 =C2=A0 ]</div><div>];=
</div><div>$p =3D new Plugin(); =C2=A0// Database is not injected</div><div=
>$gen =3D $p-&gt;populateCreditCardData($receipt);</div><div>foreach ($gen =
as $effect) {</div><div>=C2=A0 =C2=A0 // Call $db here instead of injecting=
 it.</div><div>=C2=A0 =C2=A0 // But now I have to propagate the $gen logic =
all over the call stack,</div><div>with &quot;yield from&quot;? :(</div><di=
v>=C2=A0 =C2=A0 // Effect handlers solve this by forcing an effect up in th=
e stack</div><div>trace similar to exceptions.</div><div><br></div><div>=C2=
=A0=C2=A0=C2=A0 // Dummy db result</div><div>=C2=A0 =C2=A0 $rows =3D [</div=
><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 [</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 &#39;card_product_name&#39; =3D&gt; &#39;KLARNA&#39;,</div><d=
iv>=C2=A0 =C2=A0 =C2=A0 =C2=A0 ]</div><div>=C2=A0 =C2=A0 ];</div><div>=C2=
=A0 =C2=A0 $gen-&gt;send($rows);</div><div>}</div><div><br></div><div>// Re=
ceipt item now has card_product_name populated properly.</div><div>print_r(=
$receipt);</div><div><br></div><div>---</div><div><br></div><div>OK, so the=
 problem with above code is that, in order for it to work, you</div><div>ha=
ve to add &quot;yield from&quot; from the top to the bottom of the call sta=
ck,</div><div>polluting the code-base similar to what happens with &quot;as=
ync&quot; in JavaScript.</div><div>Also see the &quot;Which color is your f=
unction&quot; article [1].</div><div><br></div><div>For this design pattern=
 to work seamlessly, there need to be a way to yield</div><div>&quot;all th=
e way&quot;, so to speak, similar to what an exception does, and how</div><=
div>effect handlers work in OCaml [2].</div><div><br></div><div>The questio=
n is, would this be easy, hard, or very hard to add to the</div><div>curren=
t PHP source code? Is it conceptually too different from generators?</div><=
div>Would it be easier to add a way to &quot;jump back&quot; from a catched=
 exception</div><div>(kinda abusing the exception use-case, but that&#39;s =
how effect handlers work,</div><div>more or less)?</div><div><br></div><div=
>Thanks for reading :)</div><div><br></div><div>Olle</div><div><br></div><d=
iv>---</div><div><br></div><div>[1] -</div><div><a href=3D"https://journal.=
stuffwithstuff.com/2015/02/01/what-color-is-your-function/" target=3D"_blan=
k">https://journal.stuffwithstuff.com/2015/02/01/what-color-is-your-functio=
n/</a></div><div><br></div><div>[2] - <a href=3D"https://ocaml.org/manual/5=
.3/effects.html" target=3D"_blank">https://ocaml.org/manual/5.3/effects.htm=
l</a></div></div></blockquote><div><br></div><div>You want to jump out of t=
he current stack frame to one a higher one, and possibly resume execution?<=
/div><div><br></div><div>The best way to do that is to use fibers. They bas=
ically do exactly this behavior.=C2=A0</div><div><br></div><div id=3D"m_245=
8363863665578536sig121229152">=E2=80=94 Rob</div></div></blockquote></div>

--00000000000049902b0637b22701--