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Date: Sun, 14 Apr 2019 18:52:04 +0200
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To: PHP internals <internals@lists.php.net>
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Subject: Re: [RFC] Arrow functions / short closures
From: nikita.ppv@gmail.com (Nikita Popov)

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On Mon, Apr 8, 2019 at 4:06 PM Nikita Popov <nikita.ppv@gmail.com> wrote:

> On Wed, Mar 13, 2019 at 4:56 PM Nikita Popov <nikita.ppv@gmail.com> wrote:
>
>> Hi internals,
>>
>> Motivated by the recent list comprehensions RFC, I think it's time we
>> took another look at short closures:
>>
>> https://wiki.php.net/rfc/arrow_functions_v2
>>
>> This is based on a previous (withdrawn) proposal by Levi & Bob. It uses
>> the syntax
>>
>>     fn($x) => $x * $multiplier
>>
>> and implicit by-value variable binding. This example is roughly
>> equivalent to:
>>
>>     function($x) use($multiplier) { return $x * $multiplier; }
>>
>> The RFC contains a detailed discussion of syntax choices and binding
>> modes.
>>
>> Regards,
>> Nikita
>>
>
> Heads up: I plan to start voting on this RFC tomorrow if nothing new comes
> up.
>
> Most of the discussion was (as expected) about the choice of syntax.
> Ultimately I think there are many reasonable choices we can make here, but
> we should stick to a specific proposal for the purposes of the RFC vote.
> None of the given arguments convinced me that some other syntax is
> *strictly* better than the proposed fn($x, $y) => $x*$y -- it's more a
> matter of some choices being slightly better in one case and slightly worse
> in another. My personal runner-up would be \($x, $y) => $x*$y, but I
> suspect that there are some people who are more strongly biased against
> "sigil salad" than I am...
>
> Nikita
>

So, there's been quite a bit of extra discussion here... unfortunately I
can't say that it really clarified anything, we're still circling around
different syntax choices, with the main contenders being fn, \ and ==>.

fn($x) => $x
fn($x, $y) => $x*$y

\$x => $x
\($x, $y) => $x*$y

$x ==> $x
($x, $y) ==> $x*$y

I think the main qualities of these possibilities are:

 * Implementation complexity: fn and \ are easy, ==> is hard (lexer hack).
 * Availability of reduced syntax: \ an ==> have a special single-argument
syntax, fn doesn't.
 * Obviousness/readability: fn and ==> are obvious, while \ is not.
Especially \$x => $x looks quite obscure to the uninitiated (is that a
variable escape, like it would be in strings?)

At this point I'm considering to either a) move forward with fn() as the
choice I'd consider most likely to gather a consensus or b) have a
secondary three-way vote between these three syntax choices.

Nikita

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