IR 2105 Can't declare an alias of a character literal without using expanded name

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VHDL Issue Number:        2105

Language_Version          VHDL-2002
Classification            Language Modeling Enhancement or Deficiency
Summary                   Can't declare an alias of a character literal without using expanded name
Relevant_LRM_Sections     4.3.3, 6.1
Related_Issues            
Key_Words_and_Phrases     alias, character literal
Authors_Name              Peter Ashenden
Authors_Phone_Number      +61 414 709 106
Authors_Fax_Number        
Authors_Email_Address     peter@ashenden.com.au
Authors_Affiliation       Ashenden Designs
Authors_Address1          
Authors_Address2          
Authors_Address3          

Current Status:           Submitted

Superseded By:

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Date Submitted:           7 December 2006
Date Analyzed:
Author of Analysis:
Revision Number:          0
Date Last Revised:

Description of Problem
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The syntax rules prevent a character literal being used by itself as
the name in an alias declaration. For example, it is not legal to
write
    
      alias low is '0'[return bit];
    
    The rule for name in 6.1 allows a simple name or an operator
    symbol, but not a character literal. The above would have to be
    written using an expanded name, such as
    
      alias low is STANDARD.'0'[return bit];
    
    since the suffix of an expanded name can be a character literal.
    
    Similarly, the following is illegal:
    
      type T is ('a', 'b', 'c');
      alias 'A' is 'a'[return T];
    
    Assuming this was in an enclosing regional named R, the alias would have to be written as
    
      alias 'A' is R.'a'[return T];

Proposed Resolution
-------------------

Augment the BNF rule for name in 6.1 to include character_literal as
an alternative. This would mirror other places where simple_name and
operator_symbol are alternatives for a designator (such as in the
entity tag of an attribute specification).

VASG-ISAC Analysis & Rationale
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TBD

VASG-ISAC Recommendation for IEEE Std 1076-2002
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TBD

VASG-ISAC Recommendation for Future Revisions
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TBD


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