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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>
Cc: Greg Stark <stark@mit.edu>
Cc: Erik Rijkers <er@xs4all.nl>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Daniel Verite <daniel@manitou-mail.org>
Cc: Jim Nasby <Jim.Nasby@bluetreble.com>
Cc: PostgreSQL <pgsql-hackers@postgresql.org>
Cc: pgsql-hackers-owner@postgresql.org
Subject: Re: \if, \elseif, \else, \endif (was Re: PSQL commands: \quit_if, \quit_unless)
Date: Wed, 22 Feb 2017 18:15:01 -0500
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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.

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  To: pgsql-hackers@postgresql.org
  Cc: corey.huinker@gmail.com, tgl@sss.pgh.pa.us, coelho@cri.ensmp.fr, stark@mit.edu, er@xs4all.nl, robertmhaas@gmail.com, daniel@manitou-mail.org, Jim.Nasby@bluetreble.com, pgsql-hackers-owner@postgresql.org
  Subject: Re: \if, \elseif, \else, \endif (was Re: PSQL commands: \quit_if, \quit_unless)
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