Re: How come Ada isn't more popular?

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

Markus E Leypold
<development-2006-8ecbb5cc8aREMOVETHIS@ANDTHATm-e-leypold.de> writes:

> If yout have only downward scopes for "closures" and memory allocation
> this will, finally, interact badly with the fact that "implicit
> (i.e. static type safe) casting" of classes is also only possible
> downwards. My impression is, that all these things together rule out
> some useful designs, that would otherwise possible. Or to say it
> differenty: Object orientation w/o indeterminable scopes, upward
> closures and GC doesn't work well. Some abstractions cannot be
> implemented.

Why do we call these closures "downward" and "upward" instead of the
other way around?  A downward closure (allowed in Ada 2005, and to some
extent in Ada 83) is a procedure that is passed IN to another procedure,
which is toward the TOP of the call stack (up!).  An upward closure (not
directly supported in Ada, but supported in Lisp et al) is a procedure
that is passed OUT (return value, 'out' parameter, setting a global
variable) -- which means it's being passed DOWN toward the BOTTOM of the
call stack.  (Of course, the call stack is not quite a stack anymore, if
upward closures are allowed!)

It seems to me "inward" and "outward" closures would be clearer
terminology, for what are normally called "downward" and "upward",
respectively.

- Bob