module llist_mod
  implicit none

  type, private :: entry
     real, dimension (:), pointer  :: g
     double precision              :: gn
     type (entry),        pointer  :: next
  end type entry

  type list
     private
     type (entry), pointer :: first
     type (entry), pointer :: current
     integer    :: depth
  end type list

contains

  function llist_init () result (l)
    type (list)  :: l

    allocate (l % first)
    l % depth = 0
    call llist_rewind (l)
  end function llist_init

  subroutine llist_rewind (l)
    type (list)  :: l
    l % current => l % first
  end subroutine llist_rewind

  function llist_depth (l) result (n)
    type (list)  :: l
    integer      :: n

    n = l % depth
  end function llist_depth

  subroutine llist_add (l, g, gn)
    type (list)                   :: l
    real, dimension (:), pointer  :: g
    double precision, intent (in) :: gn

    l % current % g => g
    l % current % gn = gn
    allocate (l % current % next)
    l % depth =  l % depth + 1
  end subroutine llist_add

  subroutine llist_down (l, g, gn)
    type (list)                   :: l
    real, dimension (:), pointer  :: g
    double precision              :: gn

    g => l % current % g
    gn = l % current % gn
    l % current => l % current % next
  end subroutine llist_down

  subroutine llist_close (l)
    type (list)  :: l
    integer      :: i

    do i = 1, l % depth
       call llist_chop (l)
    end do

    deallocate (l % first)
  end subroutine llist_close

  subroutine llist_chop (l)
    type (list) :: l

    call llist_rewind (l)
    l % first =>    l % current % next
    if (associated (l % current % g)) &
    deallocate (l % current % g)
    deallocate (l % current)
    l % depth = l % depth - 1
  end subroutine llist_chop

end module llist_mod