To append some things to some other things:
Put the things' first into a thing.
If the thing is nil, exit.
Remove the thing from the things.
Append the thing to the other things.
Repeat.

To prepend some things to some other things:
Get a thing from the things (backwards).
If the thing is nil, exit.
Remove the thing from the things.
Prepend the thing to the other things.
Repeat.