gistfile1.txt

use nqp;
my str $string = "this,that,other,thing," x 100;
my int $chars = nqp::chars($string);
my $i := nqp::add_i(0,0);
$i := nqp::add_i(0, 50);
nqp::while(nqp::isle_i($i, $chars), (
    $string = nqp::replace($string, nqp::index($string, ',', $i), 1, ",\n");
    $i := nqp::add_i($i, 50);
  )
);
say $string;