Re: [RFC] [VOTE] Short Closures

"Anthony Ferrara" wrote in message news:CAAyV7nHVNGG8yOyGhTE=pKACi4GDTgrdVcS4RDXb2fLmNy4Zpg@mail.gmail.com...

Dmitry, On Tue, Sep 22, 2015 at 3:19 PM, Dmitry Stogov <dmitry@zend.com> wrote:

On Tue, Sep 22, 2015 at 9:20 PM, Anthony Ferrara <ircmaxell@gmail.com> wrote:

Dmitry, On Tue, Sep 22, 2015 at 2:05 PM, Dmitry Stogov <dmitry@zend.com> wrote:

On Tue, Sep 22, 2015 at 7:01 PM, Bob Weinand <bobwei9@hotmail.com> wrote:

Am 22.09.2015 um 17:36 schrieb Dmitry Stogov <dmitry@zend.com>: On Tue, Sep 22, 2015 at 4:54 PM, Joe Watkins <pthreads@pthreads.org>

wrote:

I'd really like to understand what you're trying to say there Dmitry,

but

I don't get it. What is your example function trying to show ? As it mentions in the RFC, vars in short closure are by-value, so I

can't

see what side effects you might be thinking of ?

It's clear to me that foo() will return NULL, but how many warnings about unused variable $y will we get? Thanks. Dmitry.

Cheers Joe On Tue, Sep 22, 2015 at 9:25 AM, Dmitry Stogov <dmitry@zend.com> wrote:

I'm against the magic - "automatically use () all of the (compiled) variables". I'm also against compound short closures with curly brackets. in my opinion they opens too many ambiguous questions. function foo() { (($x) ~> {$y = 3; return $y + $x;})(5); return $y; } also think about nested closures and use of variables from not direct enclosure. I'm not sure if we need all "functional programming" features in PHP,

but

if we introduce them, lets do it consistently with the existing

language.

I think, this proposal can't be approved without support for type

hinting.

Thanks. Dmitry. On Tue, Sep 22, 2015 at 4:59 AM, Bob Weinand <bobwei9@hotmail.com>

wrote:

Hey, Thanks for all your feedback in the discussion thread! So, before I start the vote, just two quick notes: I've added two notes about the statement syntax and the single

variable

use. Though a few people complained, I'm not switching to the ==> operator,

as

I noticed many people expected typehints to work (they don't due to

parser

limitations) when they compared to Hack's short Closures. It also

allows us

to differ syntax-wise [e.g. for typehints] from Hack without causing

any

confusion later. Which should be the smartest choice: Avoid conflicts.

(If

anyone strongly feels against that, he may vote no, but I would like

to

not

bikeshed that in this Vote thread, but leave it free for eventual

actual

issues.) Now, the link to the RFC about Short Closures: https://wiki.php.net/rfc/short_closures or straight ahead to the vote: https://wiki.php.net/rfc/short_closures#vote Thanks, Bob

Notice: Undefined variable: y in php shell code on line 3 It just yields exactly one notice about the inexistent $y (as it obviously does not leak through the scope): by-value binding. I'm not sure what your issue here is?

The current PHP version emits two warning on similar constructs, and this is explainable because we explicitly "use" $y. $ sapi/cli/php -r 'function foo(){(function($x) use ($y){$y=3; return $y+$x;})(5);return $y;} var_dump(foo());' PHP Notice: Undefined variable: y in Command line code on line 1 PHP Notice: Undefined variable: y in Command line code on line 1 NULL

There's an important distinction here. The explicit use($y) triggers a notice because you said to use an undefined variable. function foo() { (($x) ~> {$y = 3; return $y + $x;})(5); return $y; } In this case, there's no practical binding of $y at all. The $y in the scope of the closure is never actually read from before it is assigned to. Meaning the variable doesn't need to exist prior to that assignment, meaning that it doesn't have to be bound (used), and as such shouldn't throw a notice.

This is not the way like PHP works and the proposed patch didn't change this. It produced warning on "implicit" use. Now Bob seems to fixed this by hiding the warning.

This becomes a ton easier if we ever move to an explicit CFG+SSA compile step. Then, we can see which variables dominate the closure to see what needs to be bound vs what doesn't. In this example, converted to SSA, you'd see: function foo() { $y1 = 12; (($x1) ~> {$y2 = 3; return $y2 + $x1;})(5); return $y1; } Hence you can see that $y2 is truly an independent variable, and hence $y1 never needs to be bound (and hence no notice). So your case of explicitly using $y isn't actually what's happening with the closure (at least with respect to userland behavior). Hence why the lack of notice exists. My $0.02 at least,

This is interesting, and I also thought about this. But this is going to be different language with different rules. Also, this approach can't handle all possible cases in dynamic languages, where we can't say if variable is used or assigned first. function foo() { $y = 1; $f = ($x) ~> {

    for ($i = 0; $i < 2; $i++) {
       if ($x) {
         $y = 5;
       } else {
         echo $y
       }

}; $f(0); $f(1); } Your approach won't be able to determine if $y in short closure is local variable or from function foo(). Anyway, this is not related to Bob's proposal.

Yes it can. Because the usages of $y are not fully dominated by an assignment, there is at least one path from $y = 1 to echo $y that exists (this is trivial to prove). Hence the binding would need to happen (no matter if that path was chosen by the actual execution path). Variable-variables would need to be taken into account, but that would be easy to solve by saying if we see a Var-Var usage, bind everything unless we can prove the variable is dominated inside the lambda. And this is related to Bob's proposal in a way. Right now, he has to bind every symbol that exists in the closure using a non-notice read (if it exists in the parent, bind, otherwise don't notice). The point I was making is that if we modify our compiler it can get even smarter, reducing the cases where we over-bind (and thereby making it more efficient). Considering that some people are concerned around the performance implications of the binding, possible solutions to that problem do exist and could be implemented. Anthony

The more I read of this thread the more I think that it is a totally bad idea. If a single line of code requires a whole page to describe what it does, and even then there is a great deal of confusion between different people, then I would class that line of code as "unreadable". By this I mean that if I cannot determine within 5 seconds what a line of code does with complete accuracy then it becomes a maintenance nightmare. The objective of "good" programming is NOT to write code with as few keystrokes as possible, it is, as Abelson and Sussman wrote in 1944, "Programs must be written for people to read, and only incidentally for machines to execute". Martin Fowler, the author of Patterns of Enterprise Application Architecture, wrote "Any fool can write code that a computer can understand. Good programmers write code that humans can understand. " Please please please STOP with this nonsense about writing small amounts of clever code and stick with writing simple but readable code. I would much rather see 5 separate instructions on 5 separate lines than 5 instructions squeezed into a single line. IMHO the readability of a piece of code is directly proportional to the number of keystrokes used to write it. In other words, less keystrokes equals less readability. -- Tony Marston