sub tux_recur { my ($length, $ones) = @_; $length or return []; $ones or return [ "0" x $length ]; $ones == $length and return [ "1" x $length ]; [ ( map { "0$_" } @{tux_recur ($length - 1, $ones )} ), ( map { "1$_" } @{tux_recur ($length - 1, $ones - 1)} ), ]; }