Horton

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

Corey Huinker <corey.huinker@gmail.com>

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From: Corey Huinker <corey.huinker@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Fabien COELHO <coelho@cri.ensmp.fr>, Greg Stark <stark@mit.edu>, Erik Rijkers <er@xs4all.nl>, Robert Haas <robertmhaas@gmail.com>, Daniel Verite <daniel@manitou-mail.org>, Jim Nasby <Jim.Nasby@bluetreble.com>, PostgreSQL <pgsql-hackers@postgresql.org>, pgsql-hackers-owner@postgresql.org
Date: 2017-02-22T23:15:01Z
Lists: pgsql-hackers 
On Wed, Feb 22, 2017 at 5:59 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Ah, I see why *that* wants to know about it ... I think.  I suppose you're
> arguing that variable expansion shouldn't be able to insert, say, an \else
> in a non-active branch?  Maybe, but if it can insert an \else in an active
> branch, then why not non-active too?  Seems a bit inconsistent.
>

The major reason was avoiding situations like what Daniel showed: where
value of a variable that is meaningless/undefined in the current
false-block context gets expanded anyway, and thus code inside a false
block has effects outside of that block. Granted, his example was
contrived. I'm open to removing that feature and seeing what breaks in the
test cases.

Commits

  1. Support \if ... \elif ... \else ... \endif in psql scripting.

  2. Add a "void *" passthrough pointer for psqlscan.l's callback functions.