Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:114451
User-Agent: Cyrus-JMAP/3.5.0-alpha0-448-gae190416c7-fm-20210505.004-gae190416
Mime-Version: 1.0
Message-ID: <a9df6d2a-6d7d-4213-8a64-6da931b421fb@www.fastmail.com>
In-Reply-To: 
 <CAOWwgp=g0SFj+SJpXVM3dT+MF+SPk8GA8W8102s7LRTeWrGhZA@mail.gmail.com>
References: <f3d20496-c560-42b7-9a0d-8672b3cafa7d@www.fastmail.com>
 <df6d13a3-dfe6-44f4-a9eb-0fd065faf767@www.fastmail.com>
 <CAOWwgpmo-2ykSGQ-LjcScsvNw8=ZJf81pa0QQnMCj7XKZVxmpA@mail.gmail.com>
 <5650fab5-6006-4af2-b337-9e4aba67bf04@www.fastmail.com>
 <CAOWwgp=QLLxXfDLeFVWF2C9tn6ZcB2tDx=acn6EG1uRTMy8QjQ@mail.gmail.com>
 <13142d57-f901-462c-a38f-b146ab36497a@www.fastmail.com>
 <CAOWwgp=g0SFj+SJpXVM3dT+MF+SPk8GA8W8102s7LRTeWrGhZA@mail.gmail.com>
Date: Wed, 12 May 2021 11:18:51 -0500
To: "php internals" <internals@lists.php.net>
Content-Type: text/plain
Subject: Re: [PHP-DEV] [RFC] Partial function application
From: larry@garfieldtech.com ("Larry Garfield")

On Wed, May 12, 2021, at 4:51 AM, Nicolas Grekas wrote:

> > > This makes me wonder: can we create a partial programmatically? Wouldn't
> > > that be needed for some use cases?
> > > Partial::createFromCallable($callable, the-args)?
> > >
> > > Nicolas
> >
> > I cannot think of a use case where that would be needed.  Since you can
> > partial-ize any callable, including a dynamic one, if you needed to do
> > something like partial-ize one of a series of function calls you can do
> > that already:
> >
> > $c = match($some_input) {
> >   'A' => 'func_a',
> >   'B' => 'func_b',
> >   'C' => 'func_c',
> > };
> >
> > $p = $c(1, 2 ?, 4);
> >
> > Though at that point, just partialing them in the first place inside the
> > match would be better as then you never have a function name in a string to
> > begin with.
> >
> 
> Here is a use case: high-order argument resolvers / function reducers.
> 
> What I mean is a function that takes a callable as arguments, resolves as
> many args of the callable as it can using whatever logic fits, and returns
> a callable with fewer arguments (only the non-resolved ones - aka a
> Partial).

You're thinking something like an auto-wiring routine for callables?  

function volume(int $x, int $y, int $z) { ... }

class Resolver {
  private array $context = ['x' => 5];

  public resolve(callable $c) {
    foreach (get_argument_names_from_param($c) as $k) {
      if (isset($this->context[$k]) {
        $args[$k] = $this->context[$k];
      }
    }
    return $c(...$args, ?);
  }
}

$r = new Resolver();
$c2 = $r->resolve(volume(?));

print $c2(y: 3, z: 9);

I haven't tried running that (I don't feel like messing with the necessary reflection), but... I think it would work already?  Whether that's useful in practice or not I don't know. :-)

--Larry Garfield