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Subject: Re: Weird error with Dynamic_Predicate
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Date: 2014-05-12T22:59:28-06:00
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On 12-May-14 13:47, mockturtle wrote:
> Any ideas?

   -- Identifier:
   Type Identifier is new String
   with Dynamic_Predicate =>
         Validate_Identifier_String( String(Identifier) )
      or Validate_Qualified_Identifier_String( String(Identifier) );

-- Typecasting is desired so that the predicate doesn't depend on
-- the input checking the predicate and thereby infinite-looping.

-- ...

     -- Ensures conformance of identifiers.
     --
     -- EBNF:
     -- identifier ::= identifier_letter {[ "_" ] ( identifier_letter | 
digit )}
     -- identifier_letter ::= upper_case_letter | lower_case_letter
     -- digit ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
     Function Validate_Identifier_String	( Input : String ) return Boolean;

-- body

     Function Validate_Identifier_String	( Input : String ) return 
Boolean is
         Use Ada.Characters.Handling;
         Head : Character renames Input(Input'First);

         Function Underscore_Alphanumeric(C : Character) return Boolean is
           ( C = '_' or else Is_Alphanumeric(C) );

         Subtype Tail is Positive Range Input'First+1..Input'Last;

     Begin
         Return Result : Boolean := True do
             -- Ensure that Input's first character is a letter.
             -- (Implicit: that there is a first character.)
             -- (Implicit: that there is a last character.)
             Result:= Result
               and then Input'Length in Positive
               and then Is_Letter(Head);

             -- All subsequent characters must be underscor or alphanumeric;
             -- also, there can be no double underscore.
             For Index in Tail loop
                 Exit when not Result;
                 declare
                     C : Character renames Input(Index);
                 begin
                     Result := Result and Underscore_Alphanumeric( C ) and
                               (if C = '_' then Input(Index-1) /= '_');
                 end;
             end loop;

             -- The last character cannot be an underscore.
             Result:= Result and Input(Input'Last) /= '_';
         End return;
     End Validate_Identifier_String;

--------
     Validate_Qualified_Identifier_String would take its input and, upon 
detection of '.' pass the two substrings to Validate_Identifier_String 
since both would have to be valid identifiers.