! Module
module my_mod

  ! The custom operator being defined is 'plus' (Note that for some
  ! odd reason underscores are not allowed in a defined operator ie, 
  ! using 'my_plus' below wont work)

  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) ! --- Normal call to a function
  print*, z
  z = 0.0
  z = x .plus. y  ! --- Overloaded operator
  print*, z

end program main