PROGRAM quadratures

  INTERFACE
     FUNCTION integrate(ibeg, iend, myfun, p) result(value)
       IMPLICIT none
       ! beginning of integration interval
       real(kind=8), intent(in) :: ibeg
       ! ending of integration interval
       real(kind=8), intent(in) :: iend
       ! function to be integrated
       procedure(funint) :: myfun
       ! polynomial order
       integer(kind=4), intent(in) :: p
       ! result of integration
       real(kind=8) :: value
     END FUNCTION integrate
  END INTERFACE
  
  INTERFACE
     FUNCTION funint(x) result(y)
       IMPLICIT none
       real(kind=8), intent(in) :: x
       real(kind=8) :: y
     END FUNCTION funint
  END INTERFACE

  procedure(funint), pointer :: ptr

  ptr => my_exp

  write(*,*) my_exp(2.0_8)
  
CONTAINS

  FUNCTION my_exp(x) result(y)
    real(kind=8), intent(in) :: x
    real(kind=8) :: y
    y = exp(x)
  END FUNCTION my_exp
  
END PROGRAM quadratures