A simple Fortran file with submodules, a generic interface, and module procedures

main.f90

module example_mod
  use iso_fortran_env, only: wp=>real64
  implicit none

  private
  public :: fun
  interface fun
    module function fun1(x) result(y)
      real(wp), intent(in)  :: x
      real(wp)              :: y
    end function fun1

    module function fun2(x, y) result(z)
      real(wp), intent(in)  :: x, y
      real(wp)              :: z
    end function fun2
  end interface

end module example_mod

submodule (example_mod) example_smod1
  use iso_fortran_env, only: wp=>real64
  implicit none

contains

  module procedure fun1

    y = 2.d0 * x

    return
  end procedure fun1

end submodule example_smod1

submodule (example_mod) example_smod2
  use iso_fortran_env, only: wp=>real64
  implicit none

contains

  function fun2(x, y) result(z)
    real(wp), intent(in)  :: x, y
    real(wp)              :: z

    z = 2.d0 * x + y

    return
  end function fun2

end submodule example_smod2

program main
  use example_mod, only: fun
  use iso_fortran_env, only: wp=>real64
  implicit none

  print*, fun(2.d0)
  print*, fun(2.d0, 3.d0)

end program main