Bill Fellows wants you to use a built-in library method:
There are various ways to concatenate values together. A common approach I see is that people will add a delimiter and then the value and loop until they finish. Then they take away the first delimiter. Generally, that’s easier coding, prepending a delimiter, than to append the delimiter and not do it for the final element of a list. Or add it and then remove the final delimiter from the resulting string.
Gentle reader, there is a better way. And has been for quite some time but if you weren’t looking for it, you might not know it exists.
You do get bonus points if you knew this existed.