>> We've discussed a couple of times allowing the parser to "interrogate"
>> the function at parse time to let it determine what the runtime tupdesc
>> will be, but I haven't been able to come up with a good way to do that.
This seems fairly unworkable to me, as in interesting cases the parser
could not find out what parameter values to pass to the function, so the
function wouldn't have enough information to know what it will return
either.
regards, tom lane