structure Queue = struct
         exception EmptyQueue;

         type 'a queue = 'a list;

         val create = nil;

         fun enqueue(x,Q) = Q@[x];

         fun dequeue(nil) = raise EmptyQueue
         |   dequeue(q::qs) = (q,qs);

         fun isEmpty(nil) = true
         |   isEmpty(_) = false;
     end;