In your print statement, $_ is undefined. Therefore, the string "@$_\n" contains only the newline. Your square brackets create a reference to an anonymous array. The text you see is the expected output when you try to print a reference. All you must do is print the variables you want. (You may use the special variable "$," perlvar to format the output.)

 } else {
        # print "@$_\n", [ @$included, $nextValue ]
        local $, = q(, );
        print  @$included, $nextValue, "\n" 
            if $currentGoal == $nextValue;
        return if $nextValue >= $currentGoal;
      }
[download]