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Date: Tue, 1 Sep 2015 15:21:25 +0100
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Subject: Re: [PHP-DEV] [RFC] [Discussion] Short Closures
From: rowan.collins@gmail.com (Rowan Collins)

Anthony Ferrara wrote on 01/09/2015 06:53:
> function partial(callable $cb) {
>      return $left ~> $right ~> $cb($left, $right);
> }

The thing that is most unreadable to me in this is the associativity. 
Someone from, say, a Haskell background might be used to mentally 
grouping X -> Y -> Z into a series of steps but to an untrained eye it 
looks almost like there's a list of terms with ~> as the separator. As I 
understand it, an expanded form would be:

return ($left) ~> { return ($right) ~> { return $cb($left, $right) } };

...which is a bit easier to mentally group, but not much prettier than 
current PHP syntax.

What about something a bit more "enclosed" but still short. A 
for-loop-style construct occured to me:

# lambda(params; expression)
lambda($a, $b; $a * $b)
lambda($x; { while(foo()) { $x ++; } return $x; })

The curly braces don't look very natural in that last example, but I'm 
not sure what else to use. Maybe just use the existing function() syntax 
if you want a block rather than an expression?

A nice expansion of this would be to have an explicit use clause without 
any extra keywords:

# lambda(params; bound vars; expression)
$double = lambda($a;; 2*$a)
$x=3; $triple = lambda($a; $x; $x * $a)

Taking one of the RFC's examples:

function sumEventScores($events, $scores) {
     $types = array_map(lambda($event;; $event['type']), $events);
     return array_reduce($types, lambda($sum, $type; $scores; $sum + 
$scores[$type]));
}


The next example benefits less if we allow only expressions, but you 
could still write this:

function reduce(callable $fn) {
     return lambda($initial; $fn;
         function($input) use ($fn, $initial) {
             $accumulator = $initial;
             foreach ($input as $value) {
                 $accumulator = $fn($accumulator, $value);
             }
             return $accumulator;
         }
     );
}


I'll leave it to others to judge if this is better or worse than the 
current proposal, just playing with ideas...

Regards,
Rowan Collins
-- 
[IMSoP]