-- (gcd.pl:18)
die sprintf "Need two integer arguments, got %d", scalar(@ARGV) unless 
set auto eval is on.
Eval result display style is tidy.
$DB::D[0] = 3
$DB::D[1] =
@{[ '3', '5' ]}
$DB::D[2] =
@{[ '3', '5' ]}
$DB::D[3] = 2
$DB::D[4] = 0
$DB::D[5] = 7
x1 (gcd.pl:9)
    my ($a, $b) = @_;
-- (gcd.pl:11)
    ($a, $b) = ($b, $a) if ($a > $b);
$DB::D[6] = 3
$DB::D[7] = 5
$DB::D[8] =
@{[ '3', '5' ]}