From bug-octave-request at bevo dot che dot wisc dot edu  Fri Apr 20 07:18:29 2001
Subject: Re: eval() tramples on __error_text__
From: Christoph Spiel <cspiel at hammersmith-consulting dot com>
To: bug-octave at bevo dot che dot wisc dot edu
Date: Fri, 20 Apr 2001 14:19:14 +0200

Applied your patch.

Now, '__error_text__' is defined in the catch-string of an eval(), but
it does not get undefined outside of it.  In fact, '__error_text__'
cannot be redefined at all.  See line :2>, where the error message
should report 'b' to be undefined.


    octave:1> eval("clear a; a;", "et = __error_text__;"); et, __error_text__
    et = `a' undefined near line 0 column 10

    __error_text__ = `a' undefined near line 0 column 10

    octave:2> try clear b; b; catch et = __error_text__; end_try_catch; et
    et = `a' undefined near line 0 column 10


For reasons beyond my imagination, the symbol '__error_text__' winds
up in in 'curr_sym_tab', but bind_builtin_constant() accesses
'global_sym_tab'.  Wiping out the definition of '__error_text__' in
'curr_sym_tab' as shown below, cures the persistence problem, but
introduces the problem of an undefined '__error_text__' in try-catch
again.


void
clear_global_error_variable (void *)
{
  delete error_message_buffer;
  error_message_buffer = 0;

  bind_builtin_constant ("__error_text__", "", true);

  symbol_record *sym_rec = curr_sym_tab->lookup("__error_text__"); // cls
  cout << "###         __error_text__ = <" << sym_rec->def().string_value()
       << ">\n";
  sym_rec->define_builtin_const("");
}


With the above clear_global_error_variable() I get the following
output (debug stuff '###' deleted):

    octave:1> eval("clear a; a;", "et = __error_text__;"); et, __error_text__
    et = `a' undefined near line 0 column 10

    __error_text__ = 
    octave:2> try clear b; b; catch et = __error_text__; end_try_catch; et
    et = 

:1> is OK, but :2> is wrong.


-chris


PS: I am writing test cases for try-catch and the two argument form of
    eval to augment the current test suite.  I'll send it to you as
    soon as we have ironed out the __error_text__ problems.

-- 
Christoph L. Spiel  <cspiel at hammersmith-consulting dot com>
Hammersmith Consulting,  web: www.hammersmith-consulting.com
Phone: +49-8022-662908, fax: +49-8022-662909



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