! Module
module my_mod
implicit none

  private ! Defaults everything to private
  public :: operator(.plus.) ! The main code can call 'my_add' indirectly 
                             ! using '.plus.' but NOT directly
  interface operator(.plus.)
     module procedure my_add
  end interface

contains
  function my_add(a,b)
    implicit none
    real, intent(in) :: a,b
    real :: my_add
    my_add = a + b
  end function my_add
end module my_mod

! Main Program
program main
  use my_mod
  implicit none

  real :: x,y,z
  x = 1.0
  y = 2.0
  !z = my_add(x,y) ! Will NOT work
  z = x .plus. y   ! Will work
  print*, z

end program main