VHDL Issue Number:      0252
Classification:         Language Definition Problem
Language Version:       VHDL-87
Summary:                Short-circuit operators don't when called as functions
Related Issues:         Superseded By IR 1054 (Andy Tsay)
Relevant LRM Sections:  7.2, 7.2.1, 7.3.3
Key Words and Phrases:  Short-circuit operators, expressions, function calls
Current Status:         Submitted
1076-1993 Disposition:  Superseded (ISAC Issues Outstanding)
Disposition Rationale:  N/A
Superseded By:          1054
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Date Submitted:         1992/03/06
Author of Submission:   Paul Menchini
Author's Affiliation:   CAD Language Systems, Inc.
Author's Post Address:  2 Davis Drive
                        P.O. Box 13036
                        Research Triangle Park, NC  27709-3036
Author's Phone Number:  (919) 990-9506
Author's Fax Number:    
Author's Net Address:   mench@clsi.com
-----------------------
Date Analyzed:          TBD
Author of Analysis:     TBD
Revision Number:        $Revision: 1.10 $
Date Last Revised:      $Date: 1995/08/04 01:45:13 $


Description of Problem
----------------------
Consider the following two expressions:

    1.  a and b

    2.  "and" (a, b)

These two expressions do not have identical semantics if the operator in
expression 1 and the operator denoted by the prefix in expression 2 denote
the same short-circuit operator.

Specifically, in expression 1, if the value of a is sufficient to determine
the entire expression's value, b is never evaluated.  In contrast, in
expression 2, b is always evaluated.

The LRM is clear on this point.  The first sentence of the last paragraph of
Section 7.3.3 states (in part):

        Evaluation of a function call includes evaluation of the actual
        parameter expressions specified in the call ....

No exception is made for function names that denote short-circuit operators.


Proposed Resolution
-------------------
Rework the language of the final paragraph of Section 7.3.3 to allow short-
circuit operators called as functions to evaluate their second argument only
as necessary to determine the value to be returned by the call.


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


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


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