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Date: Thu, 19 Jan 2017 23:08:35 +0000
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Subject: Re: [PHP-DEV] Pipe Operator v2
From: rowan.collins@gmail.com (Rowan Collins)

On Thu, Jan 19, 2017 at 5:54 AM, Levi Morrison <levim@php.net> wrote:
> I've talked to you about this RFC off-list, but I figured I should
> mention it on-list as well. I think we should make `|>` and `$$` two
> independent operators that work well together (rather than only
> together).

Firstly, Levi, can I say I really like this line of thinking at first 
sight. As long as we can avoid it becoming too cryptically Perlish...


On 19/01/2017 22:17, Ryan Pallas wrote:
>
> When you say assert the right hand side is callable, does that mean to
> call an object method, you would do [$obj, 'method']? What about functions,
> is it just the name like $str |> trim, or is it $str |> trim()?

This is a good point. The difference between the pipe operator as 
proposed by Sara and the combination of two separate operators is that 
in Sara's proposal you'd always write this:

$str |> trim($$)

But in Levi's proposal as I understand it, the right-hand side is not 
syntax, it's just constrained to be callable, so the simpler (but rather 
ugly) form would be:

$str |> 'trim'

On its own, trim($$) rather pointlessly wraps a function with one 
argument into another function, still with one argument, effectively 
short-hand for Closure::fromCallable('trim') [incidentally, fromCallable 
isn't actually listed in the documentation yet].

Since ($$) would leave a closure effectively unchanged, you could 
actually write:

$str |> trim($$)($$)($$)($$)

And interestingly, the $$ magic couldn't be used to turn a function with 
one argument into one with zero, because trim($$)($foo) actually 
executes the function.

This all feels fiddly for the same reason I dislike generators being 
introduced with "function" rather than their own keyword: it's one 
syntax hiding behind another. Which is a shame, because as I say, I 
liked the general idea.

Regards,

-- 
Rowan Collins
[IMSoP]