overloading a function as a structure

[John W. Eaton]

On  9-May-2005, Tom Holroyd wrote:

| This one's particularly nasty.
| 
| octave:1> grid.pos = 0
| usage: grid ("on" | "off")
| error: evaluating if command near line 40, column 3
| error: called from `grid' in file 
| `/usr/local/share/octave/2.1.69/m/plot/grid.m'
| 
| Matlab just tosses the definition of the grid function, and creates a 
| structure called grid.
| 
| Worse, this line:
| 
|      grid.pos = grid.pos(:,cfg.constr.expand) .* a
| 
| gets a syntax error, though in Matlab it doesn't, presumably because
| grid is defined somewhere above.  By itself it throws an error, but in 
| the context of the function it doesn't.
| 
| Is there a way to undefine a function?  "clear grid" beforehand 
| doesn't do it.

The problem is not that grid is a function, it's that it is marked as
a "command".

So if you do

  unmark_command ("grid");

then you should be able to write

  grid.pos = 0;

I see no fix for this problem that doesn't break other things.  What
should happen for

  ls . a = 2

?  If it creates a structure called "ls" with a field named "a" having
the value 2, then that seems bad if what I really wanted was to get a
listing of the files ".", "a", "=", and "2".  What if the "=" is
missing:

  ls . a 2

?  Then what should happen?  If it produces a directory listing, then
it seems we need potentially unlimited lookahead to get this right
(there could be all kinds of crazy indexing between "ls" and "=").

If you really want these things to work in a compatible way, then I
think we need a new parser for Octave, probably implemented using
something other than Bison.

As a quick workaround, you can do

  grid = [];

before you use it as a variable.  Of course, this does mean that you
need to know which names have been marked as commands, so it may not
be the most convenient solution for you.

jwe



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