DEFVARs again (was Re: MinGW version binary gobbledygook error messages?)

[John W. Eaton]

On 28-Feb-2006, David Bateman wrote:

| 2) The DEFVAR of the gnuplot variables doesn't happen till the first use 
| of gnuplot. This causes particular problems with things that use 
| automatic_replot. Try "spy(sprandn(10,10,0.2))" for example at the first 
| prompt. See the thread on DEFVAR recently for more details of the 
| potentially intrusive fix.

Yes, I'm still waiting on some comments about that.  I would really
like to fix this problem, but I'm uncertain about whether consistency
of implementation is worth the trouble it could cause.

Built-in constants are no problem.  It doesn't matter whether they are
defined internally as variables or functions since they are never
supposed to appear on the LHS of an assignment.

Built-in variables are affected, since it has been well-documented
that the way to change something like LOADPATH is to write

  LOADPATH = "new loadpath";

We currently have about 75 built-in variables.  21 are warn_*
variables that can be removed and replaced with the new warning tag
mechanishm.  Of the rest, I think the biggest problem will be with
LOADPATH, gnuplot_binary, automatic_replot, page_screen_output,
page_output_immediately, etc.  These are symbols that we have told
people to use as variables that would now have to be used
differently.

But the change has the advantage of simplifying the internals of
Octave a bit (no more lookup up built-in variables separately from
functions, for example).

This is a big change.  I'd like to see some discussion before deciding
what to do about it.  If I don't see any discussion, I might think
that everyone enthusiatically supports making the change.

jwe