Re: Ada vs Fortran for scientific applications

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Tue, 23 May 2006 17:09:03 GMT, Dick Hendrickson wrote:

> Jean-Pierre Rosen wrote:

>> Is it possible in Fortran to define three *incompatible* types Length, 
>> Time, and Speed, and define a "/" operator between Length and Time that 
>> returns Speed?
> Yes, it's possible.  There was a long thread inb c.l.f a
> year or two ago abou this.  It's a bit of a pain in the butt
> to cover all the cases.  Is E = m*c**2 the same as E=m*c*c?

Hmm, where is any problem? As I remember 2 is integer in Fortran. I hope it
can distinguish signatures ** : R x I -> R and ** : R x R -> R. Or do you
mean a geometrical explosion of variants?

> Fortran 2003 has polymorphic variables which might make it
> easier to write a complete set of units and operators.  That
> probably would lose some compile time checking.

That depends on which kind of polymorphism it is. Ada provides three forms
of:

1. generics (like C++ templates) and overloading
2. tagged types (like C++ classes)
3. discriminated types.

All three can be used for dimensioned values.

The last one is IMO the most promising, because it supports constrained
subtypes. It is similar to Positive being a constrained Integer. So, for
example, Energy can be statically constrained Dimensioned. Now, when all
constraints are statically known, the compiler can potentially remove all
run-time checks, as well as any memory overhead required to keep the
dimension at run-time.

Then there is a problem of constraint propagation. Developing a matrix
library you surely would like to have dimensioned vectors and matrices all
constrained in a "coherent" way rather than on per-element basis. I doubt
that either 1. or 2. would be able to do it in an easy way.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de