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[Octave-bug-tracker] [bug #53752] block comment compatibility

From: John W. Eaton
Subject: [Octave-bug-tracker] [bug #53752] block comment compatibility
Date: Wed, 25 Apr 2018 11:54:18 -0400 (EDT)
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0


                 Summary: block comment compatibility
                 Project: GNU Octave
            Submitted by: jwe
            Submitted on: Wed 25 Apr 2018 03:54:17 PM UTC
                Category: Interpreter
                Severity: 2 - Minor
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: Any



We currently allow block comment markers to be mixed in any combination.  So
'%{' and '#{' are equivalent as are '%}' and '#}'.  This could cause
compatibility issues.  For example, there could be some working Matlab code
that looks like this:

  block comment
  still a block comment in Matlab

and that will fail in Octave.  This could be solved by keeping track of
whether the current block comment started with '#{' or '%{' and requiring the
types of the begin and end markers to match.  But even if we did that, the
following would work in Matlab but fail in Octave:

  block comment
  nested block comment in Octave but not Matlab
sin (x);   %% some other code that should be executed.

For that problem, I suppose we could require that to be nested, the nested
block comments must all be of the same type?  Then the '#{' in the above code
would not be recognized as the beginning of a nested block comment.  But that
would require more work for the programmer who wants to comment out a block of
code.  Now they would need to check the block of code they are commenting for
existing block comments, and then use the same style.

A far simpler solution would be to only allow block comments to use '%{' and
'%}' instead of also allowing '#{' and '#}'...

I haven't seen any bug reports about this problem occurring in real code, so
I'm marking the severity as minor and the priority as low.


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