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Postings from December 2010
demerphq wrote:
>The whole idea is to have a non-refcount incremented identifier that
>resolves to a reference to the currently executing subroutine.
This can actually be achieved without either a statically self-referential
function definition (requiring weak refs) or grubbing around in the
runtime stack. Behold, the non-recursive definition of the recursive
implementation of factorial:
my $w = sub { my($v, $x) = @_;
sub { $x->(sub { $v->($v, $x)->(@_) }, @_) } };
my $y = sub { $w->($w, $_[0]) };
my $factorial =
$y->(sub { $_[1] == 0 ? 1 : $_[1] * $_[0]->($_[1] - 1) });
print $factorial->(5), "\n";
This technique can be extended to arbitrarily many mutually-recursive
functions, an area where __SUB__/${^SUB} falls down.
(Thanks to LeoNerd for inspiring me to go in a theoretical direction.)
-zefram
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