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From: Mario Amado Alves <maa@di.fct.unl.pt>
Subject: Re: *\\~record depth~//*
Date: 1999/11/15
Message-ID: <Pine.LNX.4.10.9911151802000.11396-100000@lexis.di.fct.unl.pt>#1/1
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Date: 1999-11-15T00:00:00+00:00
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The structure may in fact happen in real problems, e.g. lexical
knowledge bases, default inheritance networks.

You know you can write

  type Component_List is array (Component'Range)

instead of

  type Component_List is array (Component'First..Component'Last)

.


On Tue, 9 Nov 1999, G wrote:

>  Message from the Deja.com forum: 
>  comp.lang.ada
>  Your subscription is set to individual email delivery
> > 
>   I am still learning (autodidactically) what is probably painfully
> silly and simple to many of you.
> However - I use the Gnat compiler to learn what is possible (though
> not necessarily sensible) in Ada.
> 
>   Some time ago Matt Heaney explained to me here that a record
> declaration
> must only contain elements which are delimited (perhaps not in those
> exact words)
>    I was playing with types tonight and I found that I could extend one
> tagged record such that I may
> include the record from which it was extended in its element list.
> 
> ----------------------------------------------------------------------------------------
> 
> package Problem is
> 
>               -- a PROBLEM is defined by its COMPONENTs and their
> ACTIONs.
> 
>   type Component is (Single, Dependent, Group);           -- for e.g.
>   type Component_List is array (Component'First..Component'Last) of
> Component;
> 
>             -- type Action is (Direct, Indirect); --
> 
>   type Simple_Problem is tagged
>   record
>     Unit : Component;          --  a Unit
>   end record;
> 
>   type Complex_Problem is new Simple_Problem with
>   record
>     Simple_Structure : Component_List;          -- deeper STRUCTURE
>     Simple_Recursive_Reference : Simple_Problem;
>   end record;
> 
>   type Compound_Problem is new Complex_Problem with
>   record
>     Complex_Structure : Component_List;           -- even deeper
> STRUCTURE
>     Complex_Recursive_Reference : Complex_Problem;
>   end record;
> 
> end Problem;
> ------------------------------------------------------------------------------
> 
> I would have thought (my grasp of symbolic logic being as admittedly
> limited
> as it is) that placing a Simple_Problem within the Complex_Problem type
> would fluff with the compiler, but it didn't.  So, obviously one may do
> this sort of thing 'legally' in Ada.
> 
> Would there be any programming situations where this sort of thing would
> apply
> or is it toally irrelevant ?  If records are included within
> abstractions of themselves
> would that make it unneccessarily complex to assign properties to
> instances
> of the records/objects ?
> 
> possibility 1) - you will tell me it is totally silly
> 
> possibility 2) - you will tell me some horrendously complex tale of
> syntax and simpler ways of doing
>                       precisely the same things.
> 
> I am just wondering out loud and as I have this wonderful facility of
> communication with the
> boffins I thought I would ask.
> 
> 
> -Graeme
> -Australia
> 
> 
> 
> 
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