The state feature in Perl 5.9+ doesn't seem to work right in recursive functions. Instead of holding the previous value, a state variable comes up undefined in recursive calls. The sub foo()below shows the value of a state variable $x in recursive and non-recursive calls:

use feature 'state';

sub foo {
    my $n = shift;
    state $x = 0;
    print "x: ", $x // '-undef-', "\n";
    $x = 1;
    foo( $n - 1) if $n;
}

foo(0);
foo(0);
foo(0);
print "\n";
foo(2);
[download]

That prints:

x: 0
x: 1
x: 1

x: 1
x: -undef-
x: -undef-
[download]

The output is as expected except for the last two lines, which come from recursive calls. I woud have expected to see $x: 1 there too. The undefined value is certainly surprizing.

Is there a reasonable explanation? I think it's a bug.

Anno