Re: F77 vs. F90 in Octave

[Daniel J Sebald]

On 11/24/2014 02:52 PM, Mike Miller wrote:
> On Mon, Nov 24, 2014 at 12:28:21 -0800, Rik wrote:
> > On 11/24/2014 11:33 AM, Daniel J Sebald wrote:
> > > That is, if we want gfortran to have precedence, then we would define
> > > (using the example at the above link)
> > >
> > >            AC_PROG_F77([gfortran fl32 f77 fort77 xlf g77 f90 xlf90])
> > >
> > > So, perhaps that is a better solution than using the stream editor to
> > > replace g77.
> >
> > I think this is a fine idea.  Eliminate all the weird hacks with sed in
> > favor of just listing our preference.
>
> The main problem with listing our preferred compiler like this is that
> it discards the curated list of supported compilers that Autoconf
> gives us today. So from a portability point of view, we would be
> throwing away the autodetection of xlf95, ifort, pgf95, etc, (just
> picking some random examples) that we inherit from Autoconf.
>
> There is no way (that I know of) to set our preferred compiler without
> specifying the entire list of compilers to try, to put it another way.
> Other than the bootstrap_epilogue function that we currently use.

That's correct.  But I just found out how to view what AC's preferred 
list is.  gfortran is now at the front of the list.  The fact that g77 
isn't even in their list, I think means that we don't even have to worry 
about any problem that the stream-editor epilogue script was attempting 
to solve.  That is, the comment

  ## FIXME -- we should really work to fix autoconf so that it prefers
  ## gfortran over g77 even when searching for a Fortran 77 compiler.

has been implemented apparently.


> > And I'm not sure we want to rely on luck regarding a compiler that handles
> > both F77 and F90.  I see several choices: 1) Change Jaroslav's code to be
> > F77-compliant, 2) Change the extension on Jaroslav's files to .f90, but we
> > would potentially then need to use the AC_PROG_FC macro and get that
> > working to handle the F90 stuff with a different compiler, 3) Switch
> > completely over to AC_PROG_FC, but this assumes that any compiler chosen
> > will be able to compile both F77 and F90 code, 4) force use of gfortran.
>
> I have no idea how valid it is, but Autoconf's working assumption
> seems to be that a F95 compiler will also support F90 and F77, and an
> F90 compiler will also support F77.

FORTRAN compatibility I don't know about.  I know that C has remained 
backward compatible, even going to C++.


> 5) Stick with what we have today, compile all Fortran files with
> $(F77) as if they were valid F77, and deal with problems in Jaroslav's
> code if any bugs are ever encountered and reported.

I think fixing bugs as we encounter is fine, whatever the configuration. 
 There can't be that many.

Dan