From owner-help-octave at bevo dot che dot wisc dot edu  Thu Nov 28 05:29:56 1996
Subject: Re: Feature, not bug
From: Ted dot Harding at nessie dot mcc dot ac dot uk (Ted Harding)
To: help-octave at bevo dot che dot wisc dot edu
Date: Thu, 28 Nov 1996 11:27:31 +0000 (GMT)

( Re Message From: Heber Farnsworth )
> 
> Here is a little thing I noticed which is not really a problem but could
> probably be handled better.  Suppose you type the name of a file in your
> load path which is not a function file.  I did this when I accidentally
> typed
> 
> octave:2> non2.oct
> 
> when I meant to type 'load non2.oct'.  I got the following
> 
> non2.oct =
> 
> panic: impossible state reached in file `tc-rep.cc' at line 1764
> error: Illegal instruction -- stopping myself...
> 
> This is not a problem since Octave quits nice and cleanly (thanks to good
> programming by jwe) but perhaps it could be handled better.  This would
> have been very frustrating if I had spent a long time manipulating some
> data but had not saved it.  It would be flushed because of a silly typing
> error.

This does not occur in the circumstances Heber suggests (i.e. giving the
name of a file as a command to octave, where the file extension looks like
a structure member):

    octave:25> save -binary non2.oct data_seg
    octave:26> non2.oct
    error: `non2' undefined near line 26 column 1
    error: evaluating expression near line 26, column 1
    octave:27> 

which is what I would have expected anyway. Octave stays up. Octave also
survives attempts to address structure members of variables which are not
structures ("error: invalid structure access attempted").

It DOES occur if you do it using the name of a function (user-defined or
built-in):

    octave:10> erf.oct
    erf.oct =

    panic: impossible state reached in file `tc-rep.cc' at line 1764
    error: IOT trap/Abort -- stopping myself...

So I guess that Heber had a function "non2" which generated data that he
saved to "non2.oct". The mishap, therefore, seems to be due to how octave
handles attempts to address structure members of functions. Given the
error message ("impossible state ... "), this suggests an unforeseen
case of parsing error.

On the other hand, octave does manage to trap attempts to define
"structure-like" function names:

    octave:3> function y = non2.oct(x)
    parse error:

    >>> function y = non2.oct(x)
                         ^


Cheers,
Ted.                                    (Ted dot Harding at nessie dot mcc dot ac dot uk)