>>660　Perl5 普通のloop版
use feature qw{current_sub say};
for (qw{321 910 909 0 11111 123456789}) {
$a = $_;
$s = 1;
@d= ();
do {
$d = int $a / 10*$s;
$m = $a % (10*$s);
unshift @d, $m*$s;
$s *= -1;
$a = ($a - $m)/10;
} while $a;
say "$_ $d => ", @d;
}

>>660　Perl5 無名関数の末尾再帰版
use feature qw{say};
for (qw{321 910 909 0 11111 123456789}) {
$s = 1;
say "$_ $d => ", sub {
$a = shift;
$d = int $a / 10*$s;
$m = $a % (10*$s);
my $ms = $m*$s;
$s *= -1;
$a = ($a - $m)/10;
(($a ? __SUB__->($a) : ()), $ms);
}->($_);
}