VHDL Issue Number:      0104
Classification:         Language Definition Problem
Language Version:       VHDL-87
Summary:                Can unary operators be used as type-conversion
                        functions?
Related Issues:         None.
Relevant LRM Sections:  4.3.3.2, 7.2, 7.3.3
Key Words and Phrases:  Predefined operators, type-conversion functions
Current Status:         Submitted
1076-1993 Disposition:  Bugs Fixed, Enhancements Outstanding (No ISAC Issues)
Disposition Rationale:  
Superseded By:          N/A
-----------------------
Date Submitted:         1991/02/11
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:          TBD
Author of Analysis:     TBD
Revision Number:        $Revision: 1.9 $
Date Last Revised:      $Date: 1995/05/13 19:34:42 $


Description of Problem
----------------------
Can operators be used as type-conversion functions?  If so, then can operation
notation be used in the formal or actual part of an association involving type
conversion?

By way of illustration, consider the following four association elements from
some port map.  Assume that the modes of the formals and the types of the
formals and actuals and operators are appropriate:

    1.  F => "not" (A)
    2.  F => not A
    3.  "not" (F) => A
    4.  not F => A

Associations 1 and 3 are syntactically allowed; moreover, because of recent
ISAC decisions regarding the semantic equivalence of operators and functions,
these associations should furthermore be semantically allowed.

Associations 2 and 4 are semantically identical to associations 1 and 3,
respectively.  However, they are not syntactically allowed.


Proposed Resolution
-------------------
Allow the unary operators to be used as type-conversion functions in an
association list.  Moreover, allow operation syntax to be used to specify these
operators, in addition to the currently allowed function-call syntax.  To
implement:

    1.  Specifically state in Section 4.3.3.2 that operators may be used as the
        function in a type conversion function.  (Alternatively, the
        equivalence between functions and operators could be established in
        either of Sections 7.2 or 7.3.3.)

    2.  Augment the productions for formal_part and actual_part in Section
        4.3.3.2 as follows:

                formal_part ::=
                        formal_designator
                        | *function*_name ( formal_designator )
                        | unary_operator formal_designator

                actual_part ::=
                        actual_designator
                        | *function*_name ( actual_designator )
                        | unary_operator actual_designator

    3.  Add the production for unary_operator to Section 7.2:

                unary_operator ::= + | - | abs | not


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


VASG-ISAC Recommendation for IEEE Std 1076-1987
-----------------------------------------------
TBD


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