Re: [RFC] Alternate approach to keeping convenience variables

[Andrew STUBBS <andrew dot stubbs at st dot com>]

Jim Blandy wrote:
> On 1/24/06, Daniel Jacobowitz <drow@false.org> wrote:
> > > Right, but there's no way to test for that in the scripting language.
> > > Your 'init-if-undefined' command has to be a primitive, implemented in
> > > C.  My argument was that having the variables always be present is
> > > more convenient for user-defined commands.
> > Andrew's point is that such a primitive was recently committed :-)
>
> If you want your user-defined command to print a helpful error mesage,
> you can't use that in an 'if'.  If we had some operator like
> $defined($foo), then that'd be different.

I'm not totally sure what you mean by this.

I put the following into the wavefront GDB and it works as I expected:

define defined
 set $temp = $arg0
 init-if-undefined $temp = 99999
 if $temp == 99999
  echo $arg0 not defined\n
 end
end


(gdb) defined $a
$a not defined
(gdb) defined $tpnum
(gdb)

It has its limitations, of course, but it does work. Your suggestion 
would still be better.