Automatic conditional use of compilers (and how to conditionally use macros which REQUIRE them)

[Diab Jerius <djerius@xxxxxxxxxxxxxxx>]

I have a library which can provides C, C++ and Fortran (F77) interfaces.

On systems without Fortran, I would like to have it (automatically) not 
build the Fortran interface.

The first obstacle I’ve run into is that

AC_PROG_F77

fails if no compiler is found, aborting the installation.  I’d like to 
turn that failure into something I can use in a conditional.

If it’s not possible to automatically move on from this failure, I can 
force the user to make a decision using something like this:

AC_PREREQ([2.57])
AC_INIT([cxcparam],[4.12.0.3],[yeah@xxxxxxxxx],[cxcparam])

AC_ARG_WITH([fortran],
        [AS_HELP_STRING([--with-fortran],[compile fortran interface 
library])],
        [use_fortran=$withval],
        [use_fortran=no])

AS_IF([test "x$with_fortran" != xno], [
    AC_PROG_F77
])
AC_OUTPUT

But then there are further obstacles; I would like to use the additional 
macros

  AC_F77_WRAPPERS
  AC_F77_LIBRARY_LDFLAGS
  AC_F77_FUNC(getarg,GETARG)

but they directly or indirectly REQUIRE AC_PROG_F77, so even if 
AC_PROG_F77 is wrapped in a conditional, e.g.:

AC_PREREQ([2.57])
AC_INIT([cxcparam],[4.12.0.3],[yeah@xxxxxxxxx],[cxcparam])

AC_ARG_WITH([fortran],
        [AS_HELP_STRING([--with-fortran],[compile fortran interface 
library])],
        [use_fortran=$withval],
        [use_fortran=yes])

AS_IF([test "x$with_fortran" != xno], [
    AC_PROG_F77
    AC_F77_WRAPPERS
    AC_F77_LIBRARY_LDFLAGS
    AC_F77_FUNC(getarg,GETARG)
])
AC_OUTPUT

AC_PROG_F77 will always be executed, regardless of the --without-fortran 
flag (and autoconf will warn

    configure.ac:11: warning: AC_REQUIRE: `AC_PROG_F77' was expanded 
before it was required
)

I must be missing something obvious.

Any ideas on where I’ve gone astray?

Thanks,

Diab