A gentle critque..

[Bill Baxter]

In article <e4dhnf$1l5n$1 at digitaldaemon.com>, Paulo Herrera says...
>
>Walter Bright wrote:
>> 
>> Those are good parallels, and it's good you brought that up. Working C++ 
>> legacy code is not going away and is not going to be translated to D. 
>> What will happen is *new* code will be done in D.
>
>Walter,
>I guess you have good reasons to think in this way, but my experience is 
>different.
>
>I've been in two different graduate schools and at two different 
>departments (Civil Engineering and Earth Sciences). I think the 
>situation in those departments in different to what people observe in a 
>CS department. In both places I met people that buy expensive Fortran 
>compilers not only to compile old libraries, but to write new code. I 
>know people that write large parallel codes in Fortran and that use a C 
>library (PETSc) for the core numerical routines. Most of them are young 
>researchers, so they learned Fortran few years ago. So, I don't think 
>Fortran is still around because of old legacy code or "old legacy 
>programmers".
>
>I think most of that people use Fortran because there wasn't anything 
>better for that kind of code. I think/hope D can be a viable alternative.

Yeh, my impression is that Fortran users care most about 
A) the ability to easily use the gobs of existing Fortran code thats out there
and 
B) having basic operations like C[i] = A[i] + B[i] run as fast as possible for
their given architecture.  
I seem to recall Fortran also has some other syntactic sugar that makes various
array operations easier than with C.  Not sure how important that is.

For A) nothing beats the ease of calling legacy fortran code than fortran
itself.  It's hard to beat there.  

For B) C's lack of alias-free arrays means C compilers can't optimize as
aggressively as Fortran ones.  C99 has the restrict keyword, but here it is
seven years after the C99 standard, and the big compiler vendors still don't
seem interested in implementing it.  And besides if you're using Fortran, you're
doing numerics.  Fast numerical code is pretty much the only benchmark that
matters in that world, so if you want to sell a fortran compiler, it better do a
great job on numerical code.  C compiler writers sell to a much wider variety of
folks, so the need to optimize numerics in order to make a profit is much less. 

None of the above has anything to do with whether Fortran is a great language or
not.  Its good enough to get their job done, and the costs of moving to a
different language outweigh the benefits for some folks.

And even if young researchers are using it, I suspect that that also has a lot
more do with what their professors were proficient with than the merits of the
language -- i.e. it *is* a legacy/inertia issue.  I took a few classes in the
Applied Math dept where the prof would provide a skeleton of Fortran code or
some support code in fortran and you were supposed to fill in the rest.  He said
we were free to use C or C++, but then we'd have to scrap together our own
bootstrap code.  I went with C++ but every other student in the class went with
Fortran, because it was the default path, and because the prof was more likely
to be able to provide help with the Fortran.

Er, so summing up, I'm agreeing with you Paolo, that some people aren't going to
give up on Fortran just because a better language comes along.  But mostly
because of how easy it is to call Fortran from Fortran, and because that's what
they teach to young numerical researchers.  But that's not everyone.  Some
numerics people do see the light and long for better more scalable tools and
aren't afraid to spend time learning something new.  I know at least one
dyed-in-the-wool fortran numerics guy who's writing a massive new library in C++
because he wants the modularity maintainability provided by OO abstractions.
But currently he has to put up with people saying his code is going to be slower
than the equivalent Fortran code.  If D could match Fortran for raw numeric
speed then at least that one argument would go away.  So I agree with Walter
that if D can be as good at numerics as Fortran then some, but certainly not
all, new code would be written in D.  This guy's library is a good example.  Big
new C++ code base with virtually no external dependencies.  Probably would have
been perfect for D if he had known about it -- and if D had been 1.0 when he
started -- and if there had been sufficient resources (like books) out there to
learn how to program in D.

Bill Baxter