On Fri, Dec 16, 2016 at 9:55 AM, Robert Haas <robertmh...@gmail.com> wrote:

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

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

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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