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From: lutz@iks-jena.de (Lutz Donnerhacke)
Newsgroups: comp.lang.ada
Subject: Re: Run-Time Type Assignment
Date: Wed, 28 Aug 2002 14:59:11 +0000 (UTC)
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* Robert A Duff wrote:
>Kilgallen@SpamCop.net (Larry Kilgallen) writes:
>> What is a downward closure ?
>
>The ability to pass a procedure as a parameter to a procedure.
>The "downward" means the closure is passed "down" from caller to
>callee.  This is more restrictive than the "full closures" which are
>found in Lisp and many other languages of that ilk; a full closure may
>be *returned* from a procedure, and may be assigned into a variable.
>
>GNAT supports downward closures via the 'Unrestricted_Access attribute,
>but that's not Ada (unfortunately).
>
>In Pascal, downward closures are very useful for making iterators and
>other user-defined control structures.

In Ada you use generics for this.