VHDL Issue Number:      1060
Classification:         Language Definition Problem
Language Version:       VHDL-93
Summary:                A'LEFT's result type is anomalously described.
Related Issues:         0203
Relevant LRM Sections:  14.1
Key Words and Phrases:  'LEFT, predefined attributes
Current Status:         Analyzed
-----------------------
Date Submitted:         1991/03/16
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:          1995/06/14
Author of Analysis:     Charles Swart (cswart@analogy.com)
Revision Number:        $Revision: 1.5 $
Date Last Revised:      $Date: 1995/06/14 23:30:53 $


Description of Problem
----------------------
The result type for A'LEFT is described (on page 14-3) as:

        Type of the left bound of the Nth index range of A.

The result types for A'RIGHT, A'HIGH, A'LOW, A'RANGE, and A'REVERSE RANGE are
described as:

        Type of the Nth index range of A.

This statement should also describe the result type for A'LEFT.


Proposed Resolution
-------------------
Change the description of the result type for A'LEFT to:

        Type of the Nth index range of A.


VASG-ISAC Analysis & Rationale
------------------------------
	The submitter is correct in that the result type for all four
cases should be treated the same. This IR has uncovered a slightly
deeper problem. The type of a range is not defined in the LRM, yet
it is referred to in several places:

	Section 8.9 Loop statement

"The loop parameter is an object whose type is the base type of the
discrete range."

	Section 9.7 Generate statements

"The generate parameter is a constant object whose type is the base type of 
the discrete range of the generate parameter specification."

	Section 12.4.2 Generate statements

"The type of this declaration is determined by the base type of the discrete 
range of the generate parameter."

	Section 14.1

as mentioned above.

This problem appears to be a carryover from Ada. The Ada 95 Reference
Manual has been updated to include both the type of a range and the
type of a discrete range. The Ada wording is essentially applicable to
VHDL.

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

The type of a range should be interpreted as defined below.


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

Change Chapter 14.1 as suggested by the author.

Formally define the concept of the type of a range similar to the
following:

Section 3.1 Scalar types.

Change the sentence reading:

"A range specifies a subset of values of a scalar type."

to read:

"A range specifies a subset of values of a scalar type (the
"type of the range")."

Section 3.2.1.1 Index constraints and discrete ranges.

Add a paragraph immediately following the first paragraph which reads:

"The type of a discrete_range is the type of the subtype defined by the 
subtype_indication, or the type of the range."