Re: [HACKERS] PSQL commands: \quit_if, \quit_unless

On Mon, Dec 5, 2016 at 12:32 PM, Robert Haas <robertmhaas@gmail.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

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.