Just realized that '?' means "unknown transactional status" in %x. That might cause confusion if a person had a prompt of %x%R. Is that enough reason to pick a different cue?
Argh.
"\?\.?[tfz]" seems distinctive enough. Note that %R uses "'=-*^!$( and %x uses *!?, which means that they already share 2 characters, so adding ? does not seem like a big issue if it was not one before.
Otherwise, maybe "&" or "%", but it is less about a condition.
Fair enough, it shouldn't be too confusing then.
The get_prompt() function can see the global pset, obviously, but can't see the scan_state, where the if-stack currently resides. I could give up on the notion of a per-file if-stack and just have one in pset, but that might make life difficult for whomever is brave enough to tackle \while loops. Or I could give pset a pointer to the current if-stack inside the scan_state, or I could have pset hold a stack of stacks. Unsure which way would be best.
