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Date: Mon, 13 Oct 2025 13:23:38 -0500
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Subject: Re: [PHP-DEV] [RFC] Partial Function Application v2
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From: larry@garfieldtech.com ("Larry Garfield")

On Sun, Oct 12, 2025, at 1:35 PM, Tim D=C3=BCsterhus wrote:
> Hi
>
> On 10/10/25 17:26, Larry Garfield wrote:
>>> What will happen if the original function already has a parameter na=
med
>>> $args0?
>>=20
>> It will skip over existing names.  I've updated the text accordingly.
>
> Okay. Looking at all the examples, I think it would be nice if it woul=
d=20
> not use the generic `arg` prefix, but use the original name as the=20
> prefix. For the
>
>      function foo(int $a =3D 5, int $b =3D 1, string ...$c) { }
>
> example, the 3rd and following parameters could be `$c_1`, `$c_2`, =E2=
=80=A6=20
> (still skipping over duplicates).

OK, there was a miscommunication between Arnaud and I.  It is using the =
variable name, not "args" already.  Just with no _ and 0-based.  I've up=
dated the RFC accordingly.

> Okay. Now looking at the examples:
>
>      $c =3D stuff(?, ?, f3: 3.5, p4: $point, ...);
>      $c =3D fn(int $i1, string $s2, int $m5 =3D 0): string =3D> stuff(=
$i1,=20
> $s2, 3.5, $point, $m5);
>
> and
>
>      $c =3D stuff(1, 'hi', 3.4, $point, 5, ...);
>      $c =3D fn(...$args): string =3D> stuff(1, 'hi', 3.4, $point, 5, .=
..$args);
>
> seem to be inconsistent with each other with regard to whether or not=20
> "superfluous" arguments are passed through.
>
> This might (or might not?) be explained in the =E2=80=9Cfunc_get_args(=
) and=20
> friends=E2=80=9D section, but is unexplained at the point the example =
appears.=20
> Also within the func_get_args() section, there is no explicit `...$arg=
s`=20
> in the resulting signature, but instead the desugaring uses=20
> array_slice() + func_get_args().

We talked a bit more, and decided to tighten the rules further.  I've up=
dated the RFC accordingly.  Essentially, the first example is correct, t=
he second has been changed.

If the underlying function is variadic, and ... is used in the PFA, then=
 it will accept an arbitrary number of arguments.  In any other case, on=
ly explicitly-specified arguments will be passed through.

> Thank you, I'm seeing you added an example. I've a small request to=20
> hopefully make the example more useful: It currently uses only=20
> =E2=80=9Cplaceholder=E2=80=9D parameters. It would be useful to also a=
dd one pre-filled=20
> parameter to it. I would assume that this pre-filled parameter does no=
t=20
> appear within the Closure frame, but appears with the frame for the=20
> actual function?

Updated the error dump example.

> - How does it interact with `compact()`, specifically:
>
>      $partial =3D compact(someValue(), ?);
>
> Would the `?` be able to capture a variable containing the return valu=
e=20
> of `someValue()`?

Good question!  compact(), extract(), etc. can't actually work with PFA,=
 because they operate on the ambient context, which PFA by design change=
s.  I've updated the RFC to note three incompatible core functions.  (Th=
e other is func_get_arg()). =20

--Larry Garfield