[Octave-bug-tracker] [bug #47676] Error applying multiplication-assignment operator to variable defined in script

[John W. Eaton]

Follow-up Comment #2, bug #47676 (project octave):

The problem is that the parser is interpreting the expression as a command,
equivalent to


Csb ('*=', 'fact');


You may have already discovered that if you evaluate example_1 separately
before example_0 or if you replace the call to example_1 with the contents of
that file, then you will not see the error.  That's because a script file is
parsed completely and then executed.  So when parsing example_0 by itself,
Octave doesn't know that Csb is a variable so it assumes it can be called as a
function.

I suppose we can add a special case for OP= operators so that they may be
parsed as expressions even if the LHS is not yet defined as a variable. 
However, this introduces a compatibility issue because then things like


foo += bar


will be handled differently in Matlab.

As I recall, checking to see if the symbol on the LHS is a function when
parsing the expression is not the solution because the following is supposed
to work:

Define in a file with mycmd undefined:


function foo (call_command)
  if (call_command)
    mycmd +arg1
  end
end


Then call it:


foo (0)  %% foo is parsed and there is no error for mycmd being undefined.
foo (1)  %% error for mycmd undefined


Now define


function mycmd (varargin)
  varargin
end


somewhere on the path (restarting your session) and call foo (1) again and it
should display the argument to mycmd as a string.


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