From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
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To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Corey Huinker <corey(dot)huinker(at)gmail(dot)com>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, PostgreSQL <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: PSQL commands: \quit_if, \quit_unless |
Date: | 2016-12-16 17:21:35 |
Message-ID: | CAKFQuwZJPtnbdW_rvmBXyjoUdLzoWuxZaMgrbyQqjcm1gxOgXw@mail.gmail.com |
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On Fri, Dec 16, 2016 at 9:55 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Mon, Dec 5, 2016 at 12:32 PM, Robert Haas <robertmhaas(at)gmail(dot)com>
> wrote:
> >> - possible incremental implemention steps on this path:
> >>
> >> (1) minimal condition and expression, compatible with
> >> a possible future full-blown expression syntax
> >>
> >> \if :variable
> >> \if not :variable -- maybe \if ! :variable
>
We don't presently have a unary boolean operator named "!" so adding this
variant would create an inconsistency
> So I think it would be reasonable for somebody to implement \if,
> \elseif, \endif first, with the argument having to be, precisely, a
> single variable and nothing else (not even a negator). Then a future
> patch could allow an expression there instead of a variable. I don't
> think that would be any harder to review than going all the way to #5
> in one shot, and actually it might be simpler.
I worry about the case of disallowing negation in #1 and then not getting
to #5 (in the same version) where the expression "not(var)" becomes
possible.
If the expected committed patch set includes #5 then this becomes a matter
for reviewer convenience so never mind. But if its at all possible for #5
to be punted down the road incorporating the eventual "not var" and
"not(var)" syntax into #1 as a kind of shim would seem desirable.
David J.
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