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

Hello Corey & Tom,

> What is not done:
> - skipped slash commands still consume the rest of the line
>
> That last part is big, to quote Tom:
>
> * More generally, I do not think that the approach of having exec_command
> simply fall out immediately when in a false branch is going to work,
> because it ignores the fact that different backslash commands have
> different argument parsing rules. Some will eat the rest of the line and
> some won't. I'm afraid that it might be necessary to remove that code
> block and add a test to every single backslash command that decides
> whether to actually perform its action after it's consumed its arguments.
> That would be tedious :-(. But as it stands, backslash commands will get
> parsed differently (ie with potentially-different ending points) depending
> on whether they're in a live branch or not, and that seems just way too
> error-prone to be allowed to stand.

ISTM that I've tried to suggest to work around that complexity by:
- document that \if-related commands should only occur at line start
(and extend to eol).
- detect and complain when this is not the case.
- if some border cases are not detected, call it a feature.

ISTM that Tom did not respond to this possibly simpler approach... Maybe a
"no" would be enough before starting heavy work which would touch all
other commands...

Tom?

--
Fabien.