Re: \if, \elseif, \else, \endif (was Re: PSQL commands: \quit_if, \quit_unless)

>
> However I would say yes, it should provide some feedback... This means
> probably adding a new prompt substitution "%<something>". In the worst
> case, the prompt should reflect the current stack, or at least the top of
> the task...
>

We could just issue interactive-only warnings when:
- A user types a branching condition command which sets the branch inactive
- A user types a command or query when the current branch is inactive.

The warnings could be specific about state, something like:

psql session is now in an inactive \if branch. No queries will be executed
and only branching commands (\if, \elif, \else, \endif) will be evaluated.

psql session is now in an inactive \elif branch. No queries will be
executed and only branching commands (\if, \elif, \else, \endif) will be
evaluated.

psql session is now in an inactive \else branch. No queries will be
executed and only branching commands (\if, \endif) will be evaluated.

This could of course be done in addition to prompt changes, and is
orthogonal to the CTRL-c option. I'd like more input before moving forward
on either of those, as they have a good chance to clobber other expected
behaviors.