Yes I can.

use strict;
use warnings;

use Test::More tests => 5;

my @x = 1 .. 5;

is_deeply([p( 3, 'x', @x)], [ @x ]);
is_deeply([p(-3, 'x', @x)], [ @x ]);
is_deeply([p( 7, 'x', @x)], [ @x, 'x', 'x' ]);
is_deeply([p(-7, 'x', @x)], [ 'x', 'x', @x ]);

@x = ();
is_deeply([p(-4, 'x', @x)], [ 'x', 'x', 'x', 'x' ]);


sub p {($a,$b,@x)=@_;@_=($b)x(abs@x-abs$a);@_=abs$a>@x?$a<0?(@_,@x):(@
+x,@_):@x}
[download]

Update:
oh dear, @x is a global. silly, me.