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Date: Fri, 17 Mar 2023 09:54:20 +0100
Message-ID: <CABdc3WrcpPT-HMtren5n_=M5dWiSKywzsz3ht8vbCUsgc++dfw@mail.gmail.com>
To: Larry Garfield <larry@garfieldtech.com>
Cc: php internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000c46b1805f714b9f6"
Subject: Re: [PHP-DEV] First-class callable partial application
From: michal.brzuchalski@gmail.com (=?UTF-8?Q?Micha=C5=82_Marcin_Brzuchalski?=)

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Hi Larry,

czw., 16 mar 2023 o 23:26 Larry Garfield <larry@garfieldtech.com>
napisa=C5=82(a):

> On Thu, Mar 16, 2023, at 4:14 AM, Rowan Tommins wrote:
> > On 15/03/2023 21:12, Dan Ackroyd wrote:
> >> Would it be desirable to split those two things into two separate
> >> RFCs, by having the first RFC not have native syntax support, but
> >> instead another static method on Closure? e.g. something like:
> >>
> >> Closure::partial($callable, array $position_params, array
> >> $named_params): Closure {}
> >
> >
> > Hm... now we have the first-class callable syntax, making it an instanc=
e
> > method on Closure would allow this:
> >
> > $mapFoo =3D array_map(...)->partial([$foo]);
> > $filterFoo =3D array_filter(...)->partial([1 =3D> $foo]);
> >
> > Which could copy over the full signature, so be equivalent to this:
> >
> > $mapFoo =3D static fn(array ...$arrays): array =3D> array_map($foo,
> ...$arrays);
> > $filterFoo =3D static fn(array $array, int $mode =3D 0): array =3D>
> > array_filter($array, $foo, $mode);
> >
> > While being a similar length to a much less rich version:
> >
> > $mapFoo =3D fn($array) =3D> array_map($foo, $array);
> > $filterFoo =3D fn($array) =3D> array_filter($array, $foo);
>
> Fascinating!  I... don't know if we considered something like that or not
> 3 years ago.  It's been a while.
>
> It's definitely not as nice as the integrated syntax, but it does have th=
e
> advantage of the implementation almost certainly being rather pedestrian =
in
> comparison.  That approach would favor left-to-right application, but not
> force it, which is probably sufficient.
>
> As a thought experiment, if we had that syntax and functions that were
> designed to be used with them, it would look like so:
>
> function amap(callable $c, iterable $it) { ... }
> function implode(string $sep, iterable $it) { ... }
> function length(string $s) { ... }
>
> $arr =3D [1, 2, 3];
>
> $a2 =3D amap(...)->partial(chr(...))($arr);
>
> $str =3D implode(...)->partial(',')($a2);
>
> Or, if combined with pipes:
>
> $size =3D $arr
> |> amap(...)->partial(chr(...))
> |> implode(...)->partial(',')
> |> length(...);
>
> Which... is not terrible, especially as it doesn't preclude using higher
> order functions for more control.
>

Maybe we could introduce two additional methods on a Closure similar to
what Java have
https://docs.oracle.com/javase/8/docs/api/java/util/function/Function.html
* andThen() - which functionality is like a pipe operator
* apply() - which you can call without the option to bind/rebind and just
pass arguments for execution

The pipe operator can be introduced later, but we could already have the
functionality on Closure.

The above example might look readable as well:

$size =3D amap(...)->partial(chr(...))
    ->andThen(implode(...)->partial(','))
    ->andThen(length(...))
    ->apply($arr);

Cheers,
Micha=C5=82 Marcin Brzuchalski

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