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Subject: Re: OT: A bit  of Sudoku
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NNTP-Posting-Date: Fri, 13 Jun 2014 00:21:40 UTC
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Date: Thu, 12 Jun 2014 18:21:37 -0600
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Date: 2014-06-12T18:21:37-06:00
List-Id: <comp.lang.ada>

On 05-Jun-14 13:00, J-P. Rosen wrote:
> I know that not everybody likes this idea, but to me exceptions are a
> powerful programming structure, not limited to handling errors.

Indeed, you can [ab]use them to get out of otherwise sticky situations, 
like the recursion problem when defining your "=" function:

   -- Nullable access-string type.
   Type LString is Access String;

   -- Definition of "=" returns true when both sides are NULL,
   -- returns false when only one side is NULL, and behaves as
   -- normal string-equality when neither side is NULL.
   Function "=" (Left, Right: IN LString) Return Boolean is

      Function Is_Equal(Left : LString; Right : String) Return Boolean is
      begin
         Return Right = Left.All;
      exception
         When CONSTRAINT_ERROR => Return False;
      end Is_Equal;

   Begin
      Return Is_Equal(Left, Right.All);
   Exception
      When CONSTRAINT_ERROR =>
         begin
            -- If this raises CONSTRAINT_ERROR, then both were NULL.
            Return Is_Equal(Right,Left.All);
         Exception
            When CONSTRAINT_ERROR => Return True;
         end;
   End "=";