Re: Ada and Automotive Industry

[dewar@merv.cs.nyu.edu (Robert Dewar)]

In article <1996Nov8.183051.21638@ole.cdac.com>, james@cdac.com says...

>I prefer a language where if I write a statement that looks like
>it should be legal it is.

Obviously, any illegal statement in any language looks illegal to someone
who knows the language well.

Equally obviously, it is a design point that any statement which nearly
everyone who knows a language quite well thinks looks legal should be legal,
and if there are exceptions to this in Ada, there are very few. If you want
to talk about a particular case, rather than generalities fine, but the
whole point of Ada is to avoid pitfalls of the type you seem to have in mind.

Furthermore, I think you don't mean legal here, but something more informal
like works. In Ada, we prefer to have an error at compile time, than have a
case where something looks OK, but does not work.

For example, in C common pitfalls like

    x = 'a';
    if (x = 'a')    --- always true
    if (x == 'a')   --- may or may not be true
    if ("x" == "x") --- generally false

are cases of legal C constructs, where presumably the principle you are
suggesting applies, these to many people look "ok", but are perhaps not
at all "ok", where I am using "ok" deliberately as an informal word.

If on the other hand you do really mean legal, and you do really mean
that a programmer
who does not know much is the arbiter, then, from my experience, nearly
every diagnostic in Ada corresonds to something that someone thinks should
be legal.

I once had a student who appeared with a program that had the diagnostic

      else ....
      |
      >>> error, no matching "if" for this "else"

the student was very puzzled and clearly felt this should be legal. When
I explained that an IF was needed, then the student responded "Oh, shall
I put in an IF somewhere".

I assume everyone agrees this is NOT a basis for allowing else with no
matching if in a language :-).

So we are really talking levels of expertise here. Quite often you see
strong opinions from someone who knows language X very well, and is
investigating language Y, but does not know Y well yet at all, and has
trouble with Y because the X knowledge does not apply. Such a person is
not well equipped to make comments on Y yet, and their comments on Y may
well have no more validity than an experienced English speaker complaining
about "idiot Germans who don't know where the verb should go, and can't
understand sentences with the verb in what obviously ought to be a legal
position" :-)

P.S. I trust that the reference to idiot Germans here is properly understood
to reflect idiocy on the part of the mythical English person making this
silly comment (not so mythical, I have met people saying essentially
exactly that :-)