-- Copyright (c) 2010 - Seweryn Dynerowicz
-- Licensed under the Apache License, Version 2.0 (the "License");
-- you may not use this file except in compliance with the License.
-- You may obtain a copy of the License at
-- 
-- http://www.apache.org/licenses/LICENSE-2.0
-- 
-- Unless required by applicable law or agreed to in writing, software
-- distributed under the License is distributed on an "AS IS" BASIS,
-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-- See the License for the specific language governing permissions and
-- imitations under the License.

module Policy.SharedAttribute
( SharedAttr(..)
) where

import Data.Set

import Algebra.Semiring

data Attribute = A | B | C | D
  deriving (Ord, Eq, Show)

data SharedAttr = SA (Set Attribute)
  deriving(Eq, Show)

instance Semiring (SharedAttr) where
  add (SA a) (SA b) = SA (union a b)
  addId = SA empty
  mul (SA a) (SA b) = SA (intersection a b)
  mulId = SA (fromList [A,B,C,D])
