Re: Fortran 9x: time for a decision

[Steven G. Johnson]

On Sat, 2 Nov 2002, Andreas Buening wrote:
> Not really. If you have preprocessed Fortran files then "finding a
> compiler" means "finding a compiler with preprocessing". Otherwise
> that compiler is useless (and you should proceed with your search).

If you have C-preprocessed Fortran files, then they are not written in
Fortran.  I agree that preprocessed Fortran is an important language to
support and one for which I would love to see autoconf support added in
the future (perhaps via an AC_PROG_FC_CPP macro or whatever), but that's
simply not the problem I'm proposing to address right now.

> > .f90 or whatever for newer code.  Is there any F90+ compiler that doesn't
> > interpret .f90 as F90 source??
> 
> xlf90, IBM's compiler for AIX. It requires -qsuffix=f=f90.

Kate Hedstrom pointed out the same problem, grrr...  This can be dealt
with, though.

> > The general problem of finding a flag to force free-format/fixed-format
> > interpretation is an issue for another macro, I think.
> 
> This means you need a "database", one different flag for every compiler.

Nope.  You need a list of possible flags to try, and a test to see if
free-format source compiles.  Much like AC_PROG_CC_STDC, as I mentioned.

> > Ultimately, this sort of thing has to be handled by custom macros, if the
> > maintainer needs particular nonstandard language features.  Particularly
> > common needs might go into the macro repository and from there (maybe)
> > make their way into the standard autoconf.
> 
> In other words: You need a "database".

Nope, you need tests to see if a particular feature works, by trying to
compile/run something with that feature.  Much like the rest of autoconf.  
(That is, you don't need a database of systems and compilers.)

> Some compilers (like f95n) try to find out the source file format
> (fixed/free) themselves. For a "print *, 'hello, world'" test program
> this might work correctly but for a more complicated source file
> it might fail. In this case there is no possibility for autoconf to find
> out whether that compiler can really handle fixed/free format.

Coming up with feature tests can be tricky, but this is not unique to
Fortran.  It's the story of autoconf: ingenuity triumphing over insanity.  =)

(Mostly, anyway.  Only sometimes we can't distinguish the ingenuity from
the insanity.)

That said, I appreciate your comments on the variety of compiler quirks we
will need to deal with.  The odds of the initial AC_PROG_FC macros and
friends working right away for all f90+ compilers are approximately zero,
but the support will enlarge over time like every other macro.  What else
can you do?

Steven