! This program just uses the interface defined in the module
program ifce
    use something
    implicit none
    real :: a
    double precision :: b
    integer :: c

    a=do_something(a)
    b=do_something(b)
    c=do_something(c)
end program ifce

module something
    interface do_something
        module procedure do_something_i
        module procedure do_something_r
        module procedure do_something_d
    end interface do_something
contains
    function do_something_i(i) result(ii)
        integer :: i, ii
        print *, "I'm an integer"
    end function do_something_i
    function do_something_r(r) result(rr)
        real :: r, rr
        print *, "I'm a real"
    end function do_something_r
    function do_something_d(d) result(dd)
        double precision :: d, dd
        print *, "I'm a double"
    end function do_something_d
end module something