VHDL Issue Number:      0017
Classification:         Language Definition Problem
Language Version:       VHDL-87
Summary:                Can predefined operators be attributed?
Related Issues:         0012, 0014
Relevant LRM Sections:  3, 4.4, 5.1, 6.6, 7.2, 10.3
Key Words and Phrases:  User-defined attributes, attribute names,
                        predefined operators
Current Status:         ISAC-Approved
1076-1993 Disposition:  Closed (All Issues Completely Addressed)
Disposition Rationale:  All issues addressed in VHDL-93 LRM.
Superseded By:          N/A
-----------------------
Date Submitted:         1989/02/07
Author of Submission:   Paul Menchini
Author's Affiliation:   CAD Language Systems, Inc.
Author's Post Address:  P.O. Box 13036
                        Research Triangle Park, NC  27709-3036
Author's Phone Number:  (919) 361-1913
Author's Fax Number:    
Author's Net Address:   mench@clsi.com
-----------------------
Date Analyzed:          1991/03/21
Author of Analysis:     Clive Charlwood
Revision Number:        $Revision: 1.9 $
Date Last Revised:      $Date: 1995/08/02 23:45:12 $


Description of Problem
----------------------
The LRM is unclear on the semantics of associating user-defined attributes with
the predefined operators (and on functions overloading them).  Consider the
following example:

        type T is range 1 to 10;
        attribute Predefined: Boolean;
        attribute Predefined of
          "=", "/=", "+", "-", "*", "/", "mod", "rem", "abs", "**": function
          is True;

This is syntactically allowed; the entity designator of an attribute
specification may be either a simple name or an operator symbol.  However, is
the entity class _function_ appropriate to these predefined operators?  The LRM
is unclear; some places (e.g., when considering named association), the LRM
maintains a distinction between predefined operators and user-defined
functions, even when those functions overload a predefined operator.  (For
example, a user-defined "+" function may be called with named association, the
predefined operator with the same parameter and result-type profile may not.)
In Section 5.1, the LRM seems to meld the concepts.


Proposed Resolution
-------------------
Explicitly state in Section 5.1 that the entity class _function_ applies both
to user-defined functions and predefined operators.  Alternatively, introduce
a new entity class _operator_ that specifically designates predefined
operators.


VASG-ISAC Analysis & Rationale
------------------------------
This is very similar to IR0012. We will follow the same recommendation.


VASG-ISAC Recommendation for IEEE Std 1076-1987
-----------------------------------------------
Assume that the first paragraph on page 5-2:

        "The attribute designator must denote an attribute.  The entity name
         list identifies those entities that inherit the attribute, as defined
         below:"

refers to both implicit and explicit subprograms.


VASG-ISAC Recommendation for Future Revisions
---------------------------------------------
Re-word the first paragraph on page 5-2 as follows:

        "The attribute designator must denote an attribute.  The entity name
         list identifies those entities ***, both implicit and explicit,***
         that inherit the attribute, as defined below:"