Personally, I use '() when I mean "the empty list" and nil when I mean either "the false boolean" or "no value yet". It is just a matter of readability, since they're both as long to type ;)
Simply () works too, and is more than 33% shorter ;)
The following shows four ways to express the empty list, and proves that they mean the same in Arc. What's a little peculiar, however, is that one gets printed differently;
