Re: Undefined psql variables

Hello Corey,

>>> \if defined varname
>>> \if sql boolean expression to send to server
>>> \if compare value operator value
>>
>> I'm still thinking:-)
>>
>> Independently of the my aethetical complaint against having a pretty
>> unusual keyword prefix syntax, how would you envision a \set assignment
>> variant? Would \if have a different expression syntax somehow?
>
> Any further thoughts?

My current opinion:

- I'm fine if \set stays as it is, i.e. no expression.

- I agree that some client-side expressions are needed, along the
semantics suggested by Tom, i.e. definition and comparisons.

- I'm really against the prefix syntax suggested by Tom

I wish I could have an explanation about why the :?varname (or some other
variant) syntax I suggested has a "namespace" issue.

The advantage that I see is that although it is obviously ugly, it is ugly
in the continuity of the various :["'?]varname syntaxes already offered
and it allows to get rid of "defined varname" which does not look like
SQL. A second advantage is that with the "defined" proposal

\if defined var1 and defined var2 or defined var3 and sqlrt() >= ..

Would probably never work work, as it cannot be embedded in another
expression, while it would work with

\if :?var1 and :?var2 or :?var3 and ...

Moreover, I would like the condition syntax to be basically SQL & psql
variables, without explicit prefixes, with a transparent decision whether
it is evaluated client side or server side.

As client-side expressions are pretty simple, ISTM that some regex could
be used for this purpose, eg for integer and boolean comparisons:

^\s*\d+\s*(=|<>|!=|<|<=|>|>=)\s*\d+\s*$
^\s*(bool...)\s*(=|<>|!=)\s*(bool...)\s*$
^\s*(NOT\s*)?(bool...)\s*$

So that one could just write the expressions without having to tell where
it is executed, eg

\if :VERSION_NUM < 110000

Would lead to

\if 100000 < 110000

Caught by the first regex, and evaluated with a few lines of code.

--
Fabien.