(* Handlings of local labels and backpatching *) local   open Fnlib Instruct Buffcodein datatype label_definition =    Label_defined of int  | Label_undefined of (int * int) list; val label_table  = ref (Array.fromList [] : label_definition Array.array); fun reset_label_table () =  label_table := Array.array(16, Label_undefined []); fun extend_label_table needed =  let val old = Array.length (!label_table)      val new_table =         Array.array((needed div old + 1) * old, Label_undefined [])  in    Array.copy { src= !label_table, si=0, len = NONE, dst= new_table, di=0 };    label_table := new_table  end; fun define_label lbl =(  if lbl < Array.length (!label_table) then () else     extend_label_table lbl;  case Array.sub(!label_table, lbl) of      Label_defined _ =>        fatalError "define_label : already defined"    | Label_undefined L =>        let val currpos = !out_position in          Array.update(!label_table, lbl, Label_defined currpos);          case L of              [] => ()            |  _ => (* Backpatching the list L of pending labels: *)              (List.app (fn (pos,orig) =>                            (out_position := pos;                            out_long (currpos - orig)))                        L;               out_position := currpos)        end); fun out_label_with_orig orig lbl =(  if lbl = Nolabel then     fatalError "out_label: undefined label"  else if lbl >= Array.length (!label_table) then    extend_label_table lbl  else ();  case Array.sub(!label_table, lbl) of      Label_defined def =>        out_long (def - orig)    | Label_undefined L =>        (Array.update(!label_table, lbl,           Label_undefined ((!out_position, orig) :: L));         out_long 0)); fun out_label l = out_label_with_orig (!out_position) l; end;