{$mode objfpc}
unit listunit2;
interface
type
	PList=^TList;
	TList=record
		pdata:pointer;
		pprev,pnext:plist;
	end;
    TListAction=procedure(p:plist);
    TDisposeAction=procedure(p:plist);

function CreateElement(pdata:pointer):PList;

function AddFirstElement(var PH:Plist; p:plist):plist;
function AddLastElement(var PH:Plist; p:plist):plist;
function InsertElement(pprevE:Plist; p:plist):plist;

procedure ListAction(PH:Plist; action:TListAction);
procedure ListActionReverse(PH:Plist; action:TListAction);// нерекурсивно

function DeleteFirstElement(var PH:Plist):plist;
function DeleteLastElement(var PH:Plist):plist;
function DeleteElement(p:Plist):plist;

procedure DisposeList(var PH:Plist; DisposeAction:TDisposeAction=nil);
implementation

{
function CreateElement(pdata:pointer):PList;
begin
	new(result);
	result^.pdata:=pdata;
	result^.pnext:=nil;
end;

function AddFirstElement(var PH:Plist; p:plist):plist;
begin
end;

function AddLastElement(var PH:Plist; p:plist):plist;
 var _ph:plist;
begin
 result:=p;
 if ph=nil then begin ph:=p; exit; end;
 _ph:=ph;
 while _ph^.pnext<>nil do _ph:=_ph^.pnext;
 _ph^.pnext:=p; 
end;

function InsertElement(pprevE:Plist; p:plist):plist;
begin
end;

procedure ListAction(PH:Plist; action:TListAction);
begin
 while ph<>nil do begin action(ph); ph:=ph^.pnext; end;
 action(nil);
end;

procedure ListActionReverse(PH:Plist; action:TListAction);
begin
 if ph=nil then begin action(nil); exit; end; // ???
 ListActionReverse(ph^.pnext,action);
 action(ph);
end;

function DeleteFirstElement(var PH:Plist):plist;
begin
end;

function DeleteLastElement(var PH:Plist):plist;
begin
end;

function DeleteElement(pprevE:Plist):plist;
begin
end;

procedure DisposeList(var PH:Plist; DisposeAction:TDisposeAction=nil);
begin
  if ph=nil then begin 
	if DisposeAction<>nil then disposeAction(nil); 
	exit; 
  end;
  DisposeList(ph^.pnext, DisposeAction);
  if DisposeAction<>nil then DisposeAction(ph^.pdata);
  Dispose(ph);
  ph:=nil;
end;
}

end.