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From: Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>
Newsgroups: comp.lang.ada
Subject: Re: Concatenation and Characters
Date: Tue, 22 Oct 2002 14:43:37 +0000 (UTC)
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Lutz Donnerhacke <lutz@iks-jena.de> wrote:
: * Georg Bauhaus wrote:
:> o.K. it is not built into the language, but a syntactically valid
:> subprogram a la
:> 
:>   procedure fill(bowl: out glass; filled: out boolean);
:> 
:> does inform readers about a potentially unsatisfying dring?
: 
: It raises EDONTDRINKANDDRIVE.

No it doesn't :)

package drinks is
   
   EDONTDRINKANDDRIVE: exception;
   -- everyone knows this
   
   subtype up_to is float range 0.0..1.1365;
   -- filling glasses looks more honest in Britain
   
   type vessel is
     tagged record
	watermark: up_to := 0.0;
     end record;
   
   procedure refill(v: in out vessel);
   --  might raise EDONTDRINKANDDRIVE under some circumstances

   type glass is new vessel with null record;
   -- it's for humans, otherwise we might want saucers, buckets, troughs.
   -- (Or vats in case of a famous monk.) (Is it true that
   -- beer is served from tubs in some rural Irish pubs?)
   
   procedure fill(cupped: in out glass'class; filled: out boolean);
   --  `cupped` is filled iff `filled = true` on return
   
end drinks;



package body drinks is
   
   generous: constant := 0.9463;
   -- US bar keeper in continental Europe (that's
   -- _more_ than what you might get here, when comparing
   -- liquid level to glass height.)
   
   
   must_drive_home: constant boolean:= false;
   -- an accidential circumstance of life
   
   
   procedure refill(v: in out vessel) is
   begin
      if must_drive_home then
	 raise EDONTDRINKANDDRIVE;
      end if;
      v.watermark := generous;
   end refill;
   
   
   procedure fill (cupped: in out glass'class; filled: out boolean) is
   begin
      refill(cupped);
      filled := true;
   exception
      -- ... 
      when others =>  -- including EDONTDRINKANDDRIVE:
         filled := false;
   end fill;

end drinks;

-- georg