declare
class Queue
   attr queue
   prop locking

   meth init
      queue:=q(0 X X)
   end

   meth insert(X)
      lock N S E1 in
         q(N S X|E1)=@queue
         queue:=q(N+1 S E1)
      end
   end

   meth delete(X)
      lock N S1 E in
         q(N X|S1 E)=@queue
         queue:=q(N-1 S1 E)
      end
   end
end