Re: Run-Time Type Assignment

[Robert A Duff <bobduff@shell01.TheWorld.com>]

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.

- Bob