Greg Lindahl wrote:

> I'm afraid I don't get it. An integer does the job, and unlike the C
> interface, you know what the type is, so you can generate object
> files which link to any MPI implementation.
I disagree. A thing that is not an integer should not be declared as an 
integer. This caused problems in some implementations, just look at the 
source code for mpich for example. Problems arose with 64-bit 
platforms. The (default, possibly 32-bit) integer has to be converted 
by the MPI implementation into a pointer (handle), and non-thread safe 
dictionaries and other (IMO) very ugly code is used to convert the 
integers to handles and vice versa. The Fortran 90 "binding" caused 
even bigger issues...BTW, in Fortran 2008 we will allow IO units to be 
opaque handles, rather than integers, for exactly the same reasons that 
MPI handles should not be (default) integers. In any case, if you like 
integers so much talk to the MPI Forum and make the C binding use an 
integer. Then the F2003 one will also. Don't try to "fix" MPI C 
bindings inside the Fortran bindings--that is going backwards!

But anyway, I think we have a fundamental disagreement/difference here. 
You want to make this easiest for the compiler or Fortran user (compile 
one object and link to any MPI implementation). But to support such 
things requires work by both the MPI implementation team, and by the 
MPI Forum. All of this work is IMO not needed and completely a waste of 
time. Fortran (2003) can hook *directly* to the C binding, which in 
most cases is the actual language of implementation. No (or little) 
extra work done by anyone.

As a user, I find it painful than in order to get a proper MPI binding I 
need to rely on 3 different groups of people doing the "right thing" in 
time for me to use the product in my project:
1) MPI Forum needs to learn Fortran 90/2003 (which it never will, even 
90...) 
2) MPICH implementation team needs to learn Fortran, learn how various 
Fortran compilers work, and implement wrappers, scripts, etc.
3) The Fortran vendor needs to cooperate also
What I am saying allows for two simplified steps:
1) MPI Forum designs their C binding
2) MPICH implements that C binding as well as they can
From there on, I can take over.

> Why would J3 care about the MPI standard?
You are right, it would not. What I was saying is that it would care 
about whether the standard facilities it provides (C Interop) are 
designed to allow easy and standard-conforming interfacing to something 
like MPI. It is a test-case, a typical complex library that is widely 
used. As I said, interfacing to OpenGL is *much* simpler. But MPI 
brings forth a lot of issues which are more complex and require 
thinking (VOLATILE, asynchronous, side effects, derived types, 
type-genericity, rank-genericity, etc.). 

> The Fortran 77 binding is a Fortran 77 binding.
Even that one is nonconforming to the Fortran 77 standard.

Aleks