Hi!
The original anonymous functions patch[1] contained support for
__FUNCTION__ as a recursion mechanism in closures, such that I should
be able to do something like this:
$factorial = function($n) {
if ($n == 1)
return 1;
else
return $n * call_user_func(__FUNCTION__, $n - 1);
};
print $factorial(3); // => 6
You can also do it the hard way (that's how some languages not having
luxury of being PHP do it ;), using something called Y-Combinator
(http://en.wikipedia.org/wiki/Y_combinator), which allows you to unroll
recursive function into non-recursive one. This looks like this:
function Y($F) {
$func = function ($f) { return $f($f); };
return $func(function ($f) use($F) {
return $F(function ($x) use($f) {
$ff = $f($f);
return $ff($x);
});
});
}
This is the generic combinator function. Now your factorial function
would look like:
$factorial = Y(function($fact) {
return function($n) use($fact) {
return ($n == 0)?1:$n*$fact($n-1);
};
});
And then you can do just this:
var_dump($factorial(3));
Look, ma, no recursion! :)
If it looks confusing, then you're right - it is :) It may be not what
you would want to do in your code (or maybe you do), but this is yet
another thing now possible with PHP.
On the other hand, we may want to add some way to refer to the closure
currently being run. We should have this information, so it should not
be too hard to do.
--
Stanislav Malyshev, Zend Software Architect
s...@zend.com http://www.zend.com/
(408)253-8829 MSN: s...@zend.com
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