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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Callback in Ada
Date: Tue, 04 Jan 2011 14:47:42 -0500
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2011-01-04T14:47:42-05:00
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"Alex Mentis" <foo@invalid.invalid> writes:

> Since it�s the topic of discussion, and since you wrote the proposal,
> is it true that expression functions (which, in effect, appear to be
> function specifications that include small expressions as the function
> bodies), when supported, could appear in a package specification,

Yes.

One reason you might want to do that is when you call an
expression function in a precondition, and you want the compiler
or other tool to know what it does (at compile time of clients),
to help it prove things.

During the design, I argued that it's going to be annoying,
because as soon as you want a local variable inside that
function, you have to move it to the package body, weakening
the ability to prove things.  So we should simply allow
subprogram bodies in package specs.

Others argued that we don't want to give people the ability to
completely dispense with Ada's separation of spec and body.
Also, the expression function syntax is nice for short
"one liners", where the extra verbiage of "begin" and
"end Blah;" is just noise.

- Bob