Re: Alternatives to C: ObjectPascal, Eiffel, Ada or Modula-3?

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

Martin <martin.dowie@btopenworld.com> writes:

> On Jul 21, 3:09�pm, Jon Harrop <j...@ffconsultancy.com> wrote:
>> I do not doubt that. My concern about Ada is primarily that it prohibits
>> many conventional and hugely-productive mainstream abstractions like
>> first-class lexical closures. Those are particularly beneficial in the
>> context of scientific computing.
>
> But I'm afraid it does...20 years ago it didn't.

No, that's not quite right.  Ada 2005 does not have "first-class lexical
closures", as Jon said.  Ada has "downward closures" (sometimes called
"inward closures").  In Ada, you can pass a nested function to a
non-nested function.  You cannot return a nested function from the
function containing it.  Both are required, to make them "first class"
(or "full closures"), as in OCaml, Lisp, Haskell, etc.

I'd say downward closures give you at least 80% of what one might want
from closures.

Unfortunately, the syntax for downward closures is pretty awful
in Ada, compared to (e.g.) OCaml.  There are proposals to make
it better in the next version of Ada.  It is unlikely that the
next version of Ada will have full closures.  (Of course, you can
always simulate full closures in Ada, using tagged and class-wide
types, but it can get pretty ugly.)

I'd still choose Ada over OCaml for what the OP wants to do.
E.g. Ada's ability to have multiple user-defined integer
types seems like a trivial thing, but in practice it is
hugely beneficial.

For example, suppose I have an array containing indices into another
array.  Using a different index type for the two arrays makes the code
clear -- when I see an integer variable, I can immediately tell from
its type which array it is intended to index.

Both OCaml and Ada are pretty good language designs -- far better than
some of the more popular languages.  Both have advantages and
disadvantages.

I would not choose any version/dialect of Pascal or Modula for anything,
these days.  Ada is strictly better.

Eiffel is a nice language design, but suffers from some other problems.
By the way, some of the "design by contract" stuff from Eiffel has
already been implemented in GNAT (the free-software Ada compiler),
and even more is being considered for the next version of Ada.

>> > Sounds pretty scientific to me...and there are plenty others, e.g.
>> > some Astrophysics work [http://homepage.univie.ac.at/martin.stift/].
>>
>> Might be interesting to translate some of the examples in those lecture
>> notes from Ada to a more modern language.

Jon, why do you use "modern" to mean "good"?  They are not synonymous!
For example, closures are good, but they were invented a long
time ago -- they're certainly not "modern".

If you said, "Might be interesting to translate some of the examples in
those lecture notes from Ada to a language with full closures", then
I'd agree -- it would be interesting indeed.

- Bob

P.S. You should know my potential biases:  I was heavily involved in the
design of Ada 95, and somewhat involved in the design of Ada 2005,
and continue to be somewhat involved in the ongoing design of the
next version.  And I currently work for AdaCore.