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    head @ @  head @ next head !  -1 used +! ;
 </lang>
+=={{header|Fortran}}==
+{{works with|Fortran|90 and later}}
+See [[FIFO (usage)]] for an example of <code>fifo_nodes</code>
+<lang fortran>module FIFO
+  use fifo_nodes
+! fifo_nodes must define the type fifo_node, with the two field
+! next and valid, for queue handling, while the field datum depends
+! on the usage (see [[FIFO (usage)]] for an example)
+!  type fifo_node
+!     integer :: datum
+!     ! the next part is not variable and must be present
+!     type(fifo_node), pointer :: next
+!     logical :: valid
+!  end type fifo_node
+  type fifo_head
+     type(fifo_node), pointer :: head, tail
+  end type fifo_head
+contains
+  subroutine new_fifo(h)
+    type(fifo_head), intent(out) :: h
+    nullify(h%head)
+    nullify(h%tail)
+  end subroutine new_fifo
+  subroutine fifo_enqueue(h, n)
+    type(fifo_head), intent(inout) :: h
+    type(fifo_node), intent(inout), target :: n
+    if ( associated(h%tail) ) then
+       h%tail%next => n
+       h%tail => n
+    else
+       h%tail => n
+       h%head => n
+    end if
+    nullify(n%next)
+  end subroutine fifo_enqueue
+  subroutine fifo_dequeue(h, n)
+    type(fifo_head), intent(inout) :: h
+    type(fifo_node), intent(out), target :: n
+    if ( associated(h%head) ) then
+       n = h%head
+       if ( associated(n%next) ) then
+          h%head => n%next
+       else
+          nullify(h%head)
+          nullify(h%tail)
+       end if
+       n%valid = .true.
+    else
+       n%valid = .false.
+    end if
+    nullify(n%next)
+  end subroutine fifo_dequeue
+  function fifo_isempty(h) result(r)
+    logical :: r
+    type(fifo_head), intent(in) :: h
+    if ( associated(h%head) ) then
+       r = .false.
+    else
+       r = .true.
+    end if
+  end function fifo_isempty
+end module FIFO</lang>
 =={{header|Haskell}}==