module parent
real, parameter :: pi = 4.*atan(1.)
real :: tau

interface
module elemental real function pi2tau(pi)
  real, intent(in) :: pi
end function pi2tau

module subroutine good()
end subroutine good
end interface

end module parent

program main

use parent

tau = pi2tau(pi)

print *,'pi=',pi, 'tau=', tau

call good()

end program