I was thinking about this too, because we're going to eventually need to support having multiple storage devices connected, and BASIC has no concept of where the currently-loaded program came from, and the closest thing from the era was "is the correct disk inserted?".
So, the best suggestions I could come up with are:
1) If your program needs to access data files that are supposed to be bundled with it, the user will need to navigate their storage to the correct directory before running your program. I don't think there's a way around this. In this case, you could query each device for the expected filename of your data file, and when you find it, you can assume the rest of the files are there too.
1a) If the files still cannot be found, then that's awkward. This would be where you tell the user to insert the correct disk, but on the X16, you'd need to prompt the user to navigate to the correct directory, either from within the program (with a UI you provide) or by exiting.
2) If your program
doesn't need to access bundled files, but
does want to provide the ability to load and/or save (like an activity program), then it's a good idea not to make assumptions about which device is correct, nor that the device is in the correct directory. So, I think a simple file browser would be good for this.
2a) Looking for the program's default filename can provide a good
hint, but it may not be a good idea to
require the user not to rename the program file, so don't error out if you can't find it.
3) We could eventually standardize on a shared memory location for launchers to put metadata in, such as which device should be considered the "preferred" one for disk access, but it'd be up to the program to actually check for that information and react to it. Launchers should already be responsible for navigating the preferred device to a preferred directory before running the program anyway.
