(from p6i)
Larry Wall wrote:
On Thu, Feb 02, 2006 at 07:12:08PM +0100, Leopold Toetsch wrote:
: >... Anyway,
: >the P6 model of "state" is more like a persistent lexical than like
: >C's static.
:
: Sorry for my dumb question - what's the difference then? (Besides that C
: dosn't have closures ;)
That *is* the difference.
[...]
I was thinking about this discussion on p6i, and I started thinking that
there's something between "my" and state: a "state" variable that is
created/initialized on each invocation of a sub but only if it's not
already in the dynamic scope (i.e. if its not a recursive call). A
slightly silly example of its use (using "temp state" as the quantifier)
would be:
sub factorial(Int $x) {
temp state Int $result = 1;
$result *= $x;
factorial $x-1 if $x > 2;
return $result if want;
}
say factorial 6;
This code is essentially the same as any other recursive factorial
function, except that it doesn't use call-stack semantics to maintain
its state. (I know P6 will do tail recursion, but sometimes I find
myself building complex args/return values to pass state from one
iteration to the next.)
Equivalent code without this feature is:
sub factorial(Int $x) {
my Int $result = 1;
my sub fact1(Int $x) {
$result *= $x;
fact1 $x-1 if $x > 2;
}
fact1 $x
return $result;
}
Dave.
