VHDL Issue Number:      1027
Classification:         Language Definition Problem
Language Version:       VHDL-93
Summary:                REVERSERANGE should be a keyword in the language.
Related Issues:         0132
Relevant LRM Sections:  13.9, 14.1
Key Words and Phrases:  
Current Status:         Analyzed
1076-1993 Disposition:  N/A
Disposition Rationale:  N/A
Superseded By:          N/A
-----------------------
Date Submitted:         1989/06/21
Author of Submission:   Rod Farrow
Author's Affiliation:   Vantage Analysis Systems, Inc.
Author's Post Address:  42840 Christy St., Suite 201
                        Fremont, CA   94538
Author's Phone Number:  (415) 659-0901
Author's Fax Number:
Author's Net Address:   N/A
-----------------------
Date Analyzed:          1994/07/25
Author of Analysis:     John Willis
Revision Number:        $Revision: 1.2 $
Date Last Revised:      $Date: 1995/05/15 19:09:55 $


Description of Problem
----------------------
   (This IR supersedes IR 0132.)

   Identifier REVERSE_RANGE should be a keyword of the language, as is 
   RANGE, in order to prevent it from being redefined to be something else, 
   especially to keep it from being redefined to be a user-defined attribute.
   This is an acute implementation problem in the following context:
      X( A'REVERSE_RANGE )
   would be an array reference if REVERSE_RANGE has been declared as a user-
   defined attribute and has been specified for A, otherwise it could be a 
   slice if A is an array object.


Proposed Resolution
-------------------
   Make REVERSE_RANGE a reserved word in the language.


VASG-ISAC Analysis & Rationale
------------------------------

Note: The problem description above was altered to read "REVERSE_RANGE"
rather than "REVERSERANGE" as submitted.

This seems like an example of a more general case in which an expression
is ambiguous.  It seems like creating a user-defined attribute with the
same name as a predefined attribute is a bad practice, however the LRM
seems to deal elsewhere with ambiguous expressions.  This special case
does not seem to warrant an additional reserved word.  If "reverse_range"
were added as a keyword, why not "LEFT", "RIGHT", etc.


VASG-ISAC Recommendation for IEEE Std 1076-1993
-----------------------------------------------

ISAC might want to consider a note warning users of this pitfall.


VASG-ISAC Recommendation for Future Revisions
---------------------------------------------

Future revisions might want to consider a note warning users of this 
pitfall.