Using spaces in (newer) mzscript vars is asking for trouble.

But I don't want to follow your method because it has the exception of handling the "end". pika told me the cool way to cycle through a list, taking advantage of this data structure--mzscript doesn't yet have arrays :/

Let the user set your drives, separated by colons
...and you.

Now, if you want to cycle through the drives, simply

The above assumes you have more than one list item in your list however. If you wanted to check if the user only had one drive you could try something like this:

Anyhow, I guess you're using two labels to animate in transition or something.

Suppose your two labels are LabelA and LabelB

On startup, I guess you want to just
...and keep a boolean variable to tell which label is 'active':

Then try a bang such as this:


Of course, set all the label texts appropriately and instead of moving them do your transition.

It could get complicated if you wanted to remember the last 'view'. It's because of the setting of the mzscript var to the evar... So replace that *script start !varset drives $drives$ with a call to something (untested) like:
and have the var drives in a varfile.