GENERIC DEFINITION MODULE DList (T : TYPE);
(* A generic doubly linked list. *)
TYPE
  Node = POINTER TO NodeRec;
  NodeRec = RECORD
    val        : T;
    prev, next : Node;
  END;
  List = RECORD
    head, tail : Node;
    count      : INTEGER;
  END;
PROCEDURE Init(VAR l : List);
PROCEDURE Append(VAR l : List; v : T);
PROCEDURE Prepend(VAR l : List; v : T);
PROCEDURE Count(VAR l : List) : INTEGER;
PROCEDURE Get(VAR l : List; i : INTEGER) : T;
PROCEDURE Sum(VAR l : List) : T;          (* arithmetic over the formal T *)
PROCEDURE Reverse(VAR l : List);
PROCEDURE ForEach(VAR l : List;           (* a procedure parameter *)
                  visit : PROCEDURE(VAR acc : INTEGER; v : T);
                  VAR acc : INTEGER);
END DList.