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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Certified C compilers for safety-critical embedded systems
Date: 08 Jan 2004 11:46:58 -0500
Organization: The World Public Access UNIX, Brookline, MA
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"Alexandre E. Kopilovitch" <aek@VB1162.spb.edu> writes:

> Robert A Duff wrote:
> 
> > Ada functions are simply a procedure with a different calling syntax.
> 
> >From a compiler writer's viewpoint - perhaps yes.

I'm not talking about the compiler writer.

>... But certainly not from
> programmer's viewpoint - if that programmer has and uses a brain (that is,
> not just eyes and fingers). There is a well-known fact that human brain tends
> to differentiate between result-oriented and "good next step" approaches, and
> this has nothing specifically mathematical. Anyway, returning to programming,
> I suppose you will not claim that there is absolutely no difference (except
> syntax) between functional and procedural programming languages.

No, I don't claim that, although at some level they are equivalent;
you can convert a procedural program into a functional one by adding
a lot of parameter passing.

My point was just that Ada's functions are *not* functions in the
functional programming sense.  Calling them "function" is therefore
misleading.

I *do* claim that both of the following compute the same mathematical
function:

    function F(X: Integer) return Integer is
    begin
        return X**2;
    end F;

    function P(X: Integer; Result: out Integer) is
    begin
        Result := X**2;
    end P;

but use different notations at the call site.

The Oz language makes these issues a bit clearer, I think.
It has a pure-functional subset that allows either notation!
Interesting.

Now, if Ada had a way to declare pure functions, enforced by the
compiler, then I wouldn't mind calling them functions.  But that's not
what Ada's functions are.

> >  IMHO, both kinds of subprograms should have been called "procedures".
> 
> I think that these both kinds of subprograms are already called "subprograms",
> so there is no need for another common name for them.

I'm not suggesting "another" name.  I'm suggesting that a *single* name
would suffice, where Ada has three names: function, procedure,
subprogram.

- Bob