From octave-maintainers-request at bevo dot che dot wisc dot edu  Mon Feb  2 16:34:25 1998
Subject: Bug in save
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Andreas Weingessel <weingessel at ci dot tuwien dot ac dot at>
cc: octave-maintainers at bevo dot che dot wisc dot edu
Date: Mon, 2 Feb 1998 16:34:17 -0600

On 21-May-1997, John W. Eaton <jwe at bevo dot che dot wisc dot edu> wrote:

| On 21-May-1997, Andreas Weingessel <weingessel at ci dot tuwien dot ac dot at> wrote:
| 
| | When assigning a value to the variable "e" this variable can not be
| | saved. The same is true for the variable named "pi". These two
| | variables are both defined in octave, but can be overwritten.
| | 
| | Repeat-By:
| | ---------
| | 
| | octave:1> e = 5
| | e = 5
| | octave:2> save xxx e
| | warning: save: no such variable `e'
| | 
| | But "e" can be used with the new value.
| | 
| | octave:3> e+3
| | ans = 8
| | octave:4> e
| | e = 5
| 
| The problem is that built-in variables like this don't become normal
| user variables when the assignment happens.  I don't see a simple fix
| for this problem, because some built-in variables should remain
| special evan after assignment.
| 
| I don't think I'll be able to fix this for 2.0.6, but I'll try to do
| it for 2.1.

Well, it took a long time for me to see the simple fix for this
problem, but I finally did.  From the message I just sent to
bug-octave:

  The fix was to install all built-in `constants' (like i, j, e, pi,
  etc.) as functions in the symbol table (doing this simply changes the
  semantics of these symbols -- the overhead of a function call is not
  actually required to evaluate them).  The `constants' i and j have
  always been installed as functions, but the others were not.  I don't
  remember why i and j alone were special and I can't think of any
  reason that e or pi should be any different from i or j.

  The semantics for built-in variables like `do_fortran_indexing' have
  not been changed, so modifying them within a function will change the
  global symbol value.

So now, you can do this:

  $ src/octave
  Octave, version 2.0.10 (i686-pc-linux-gnulibc1).
  Copyright (C) 1996, 1997, 1998 John W. Eaton.
  This is free software with ABSOLUTELY NO WARRANTY.
  For details, type `warranty'.

  octave:1> e = 5
  e = 5
  octave:2> save xxx e
  octave:3> clear e
  octave:4> load xxx
  octave:5> e
  e = 5
  octave:6> clear e
  octave:7> e
  e = 2.7183
  octave:8> quit


Thanks,

jwe