Re: [HACKERS] 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.