Re: Building blocks (Was: Design By Contract)

[Paul Johnson <Paul@treetop.demon.co.uk>]

In article <dewar.873938975@merv>, Robert Dewar <dewar@merv.cs.nyu.edu>
writes
>Brian Rogoff said
>
><<>>In fact the Eiffel exception mechanism is superior to the Ada one
>>> because it is built on a theoretical model of software engineering.>>

As someone else pointed out, I said that, not Brian.

>This is one of the more absurd statements in what is unfortunately becoming
>a rather tedious thread. First of all, the idea that being "built on
>*a* (i.e. any old) theoretical model of software engineering" is per se
>a good thing is a bit laughable.

In the original posting I was trying to be brief.  I have since
explained about design by contract and the Eiffel exception mechanism.

>Second, of course the Ada exception mechanism is build on such a model
>also -- indeed it *is* a model itself!

If I understand you correctly, the Ada exception mechanism looks like it
does because that was how the designers designed it.  My original point
was that the Eiffel mechanism looks like it does because the theory of
software contracting required it to work that way.

Actually I don't believe that the Ada designers just threw together its
exception mechanism without thinking long and hard, and I don't think
you really meant to imply it.  However the lack of an underlying theory
on its use and contribution to program correctness definitely shows up.
Ada exceptions seem to have been designed as a way of unwinding the
execution stack without letting the programmer break the language.  The
only reason for including it in the language was that programmers often
want to do this.

Paul.

--------------------------------+---------------------------------
Paul Johnson                    | You are lost in a maze of twisty
Email: Paul@treetop.demon.co.uk | little standards, all different.
       paul.johnson@gecm.com    |