Re: [HACKERS] psql - add ability to test whether a variable exists

Any colon prefixed syntax can be made to work because it is enough for the lexer to detect and handle... so

 :{defined varname}

may be an option, although I do not like the space much because it adds some fuzzyness in the lexer which has to process it. It is probably doable, though. I like having a "?" because there is a question. Other
suggestions somehow in line with your proposal could be
 :{?varname}
 :{varname?}
what do you think?

Here is a version with the :{?varname} syntax.

--
Fabien.