type 'a t = {mutable prev : 'a t option;
            mutable next : 'a t option;
            info : 'a}

type 'a dlist = {mutable front: 'a t;
		mutable back: 'a t}

exception Bound

let next = function {next=Some obj1} -> obj1 | _ -> raise Bound
let prev = function {prev=Some obj1} -> obj1 | _ -> raise Bound

let takeNext objR = objR:=(next !objR)
let takePrev objR = objR:=(prev !objR)

let add_before v obj =
	let newObj = {prev=None;next=Some obj;info=v} in
	(match obj
	    with {prev=Some obj1} -> (newObj.prev<-Some obj1;
				    obj1.next<-Some newObj)
		| {prev=None} -> ());
	obj.prev<-Some newObj
	    
let add_after v obj =
	let newObj = {next=None;prev=Some obj;info=v} in
	(match obj
	    with {next=Some obj1} -> (newObj.next<-Some obj1;
				    obj1.prev<-Some newObj)
		| {next=None} -> ());
	obj.next<-Some newObj

(* Hmm... I'm not clear whether front is after back or before it.
    Depends on moving direction:) Let's suppose before *)

let push_back v ({back=obj} as data) = add_after v obj; data.back <- next obj
let push_front v ({front=obj} as data) = add_before v obj; data.front <- prev obj