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Date: Tue, 14 Mar 2023 14:50:40 +0100
Message-ID: <CAPzBOBNGRiT6Y5grn7FHSu9xEsqqdHEeMW1dvuQCV30sf5wE2w@mail.gmail.com>
To: Rowan Tommins <rowan.collins@gmail.com>
Cc: "internals@lists.php.net" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] First-class callable partial application
From: landers.robert@gmail.com (Robert Landers)

On Tue, Mar 14, 2023 at 1:57=E2=80=AFPM Rowan Tommins <rowan.collins@gmail.=
com> wrote:
>
> On Tue, 14 Mar 2023 at 10:39, Bob Weinand <bobwei9@hotmail.com> wrote:
>
> > Hey Rowan,
> >
> > do we actually need *positional* partial application, after a ... token=
?
> >
> > Would it not be enough, to simply forbid positional arguments after a .=
..
> > and just allow named arguments? These already have well defined positio=
n
> > independent semantics.
> >
> > There may be some desire for a single argument placeholder later on, bu=
t
> > this can be introduced later, separately.
> >
>
>
> Yes, named parameters would certainly be better than left-to-right only.
> It's definitely less elegant, though, and given that PFA is largely
> short-hand for a short closure anyway, I think conciseness is quite an
> important aim.
>
> To take a couple of the above examples, and compare existing short closur=
e,
> fully positional PFA, and named-after-placeholder PFA:
>
> $isLogger =3D fn($object) =3D> is_subclass_of($object, LoggerInterface::c=
lass,
> false);
> $isLogger =3D is_subclass_of(?, LoggerInterface::class, false);
> $isLogger =3D is_subclass_of(..., class: LoggerInterface::class,
> allow_string: false);
>
> $priceFormatter =3D fn(float $num) =3D> number_format($num, 2, ',', '.');
> $priceFormatter =3D number_format(?, 2, ',', '.');
> $priceFormatter =3D number_format(..., decimals: 2, decimal_separator: ',=
',
> thousands_separator: '.');
>
> Arguably the named param version is more explicit, but in some cases it's
> significantly longer than manually defining a closure, whereas fully
> positional PFA is always shorter.
>
> Regards,
> --
> Rowan Tommins
> [IMSoP]

Something I was partial to (pun slightly intended), when thinking
about it last summer was to put named parameters with dots following,
like this:

$isLogger =3D is_subclass_of(object_or_class..., LoggerInterface::class, fa=
lse);
// or, since this is a beginning/end partial, this is the same:
$isLogger =3D is_subclass_of(..., LoggerInterface::class, false);

$isLogger(object_or_class: $myClass);
// or
$isLogger($myClass);

$priceFormatter =3D number_format(num..., 2, ',', '.');

At least, that was what I was going to propose, according to my notes.
Looking at it 8 months later, I still kinda like it.