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From: hammondr@sunroof.crd.ge.com (Richard A Hammond)
Newsgroups: comp.lang.ada
Subject: Ada functions versus arrays (i.e. () vs [] )
Message-ID: <5619@crdgw1.crd.ge.com>
Date: 28 Feb 90 18:56:35 GMT
References: <184@trwacs.UUCP> <598@software.software.org>
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Organization: General Electric Corporate R&D Center
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In article <598@software.software.org> blakemor@software.org (Alex Blakemore) writes:
>In article <184@trwacs.UUCP> epstein@trwacs.UUCP (Jeremy Epstein) writes:
>> ... look at how Ada overloads symbols.  For
>> example, parentheses are used for parameters as well as subscripts
>> (that's something that totally confuses me as an old-time C programmer).

>This is a strength of Ada not an inconsistency.  This way you can change
>between using an array and a function to provide some info  ...

>This is consistent with some formal proof methods (like Tony Hoare's)
>which treat array references as function calls. Logically they
>have the same effect.  Mathematically a function is essentially a table
>anyway.  Of course, there is a difference when you assign to an array
>element.

...

>C has some elegance but why should the programmer have to remember
>when to use [] or () ?  just to make the compiler easier to write ?

Last point first:  I think the reason is to give the programmer a cue
to what is going on.  Remember, the goal of C is to provide constructs
which map in a straightforward way to machine code.  Thus, the C
programmer is interested in the difference between an
array reference and a function call.  Besides, functions in C have the
attributes of Ada procedures and Ada functions, i.e. the Ada
function is more limited than a C function(no out or in/out parameters).
So in C: a = b(d,e) + f; could modify the value not just of a, but of
what d and/or e pointed to (if they were access types) or d/e themselves
if they are defined via macros as more complicated objects.

In fact, the argument that "an array ref" is the same as a "function call"
is true for mathematical functions but not Ada ones.  Ada functions can
have side effects, which is a software engineering deficiency in Ada.

For that reason, I'd want to know when a function call is being made.
Even a function without parameters, which is why I like C's "foo()" better
than Ada's "foo" for calling a parameterless function.
And why I'd like to distinguish between function calls and array refs.

Please, I'm trying to discuss Ada and not Ada versus C, except that
because C does some things wrong doesn't mean you can't steal the
good ideas.

Rich Hammond