haskell - 使用 Quickcheck 测试类型类，可变数量的参数

Question

我有一个戒指类型类，它看起来像这样:

class Ring a where
  addId  :: a
  addInverse :: a -> a
  mulId  :: a
  add :: a -> a -> a
  mul :: a -> a -> a

对于这个类，我有几个实例，例如

instance Ring Matrix where ...
instance Ring Integer where ...
instance Ring Modulo where ...

为了测试这些实例，我进行了以下快速检查测试:

prop_AddId :: (Ring a, Eq a, Arbitrary a) => a -> Bool
prop_AddInv :: (Ring a, Eq a, Arbitrary a) => a -> Bool
prop_MulId :: (Ring a, Eq a, Arbitrary a) => a -> Bool
prop_AddCommutative :: (Ring a, Eq a, Arbitrary a) => a -> a -> Bool
prop_AddAssociative :: (Ring a, Eq a, Arbitrary a) => a -> a -> a -> Bool
prop_MulAssociative :: (Ring a, Eq a, Arbitrary a) => a -> a -> a -> Bool
prop_Distributive :: (Ring a, Eq a, Arbitrary a) => a -> a -> a -> Bool

我不确定如何为我的所有类实例运行这些测试用例。我找到了解决方案 here
这导致以下情况:

forallRings :: (forall a. (Ring a, Arbitrary a, Eq a) => a -> Bool) -> [IO ()]
forallRings x =
    [ quickCheck (x :: Matrix -> Bool)
    , quickCheck (x :: Integer -> Bool)
    , quickCheck (x :: Modulo -> Bool)
    ]
forallRings2 :: (forall a. (Ring a, Arbitrary a, Eq a) => a -> a -> Bool) -> [IO ()]
forallRings2 x =
    [ quickCheck (x :: Matrix -> Matrix -> Bool)
    , quickCheck (x :: Integer -> Integer -> Bool)
    , quickCheck (x :: Modulo -> Modulo -> Bool)
    ]
forallRings3 :: (forall a. (Ring a, Arbitrary a, Eq a) => a -> a -> a -> Bool) -> [IO ()]
forallRings3 x =
    [ quickCheck (x :: Matrix -> Matrix -> Matrix -> Bool)
    , quickCheck (x :: Integer -> Integer -> Integer -> Bool)
    , quickCheck (x :: Modulo -> Modulo -> Modulo -> Bool)
    ]

ringTests :: IO ()
ringTests = sequence_ $
            forallRings propAddId
            ++ forallRings prop_AddInv
            ++ forallRings prop_MulId
            ++ forallRings2 prop_AddCommutative
            ++ forallRings3 prop_AddAssociative
            ++ forallRings3 prop_MulAssociative
            ++ forallRings3 prop_Distributive

我对这个解决方案有些不满意。我发现 forAllRingsX 函数有点丑陋和重复。原因是我的测试有不同数量的参数。有没有更好的方法(即具有较少样板代码的方法)来测试所有实例？

Answer 1

我认为 typeclass 函数是这里的方法。一种简单的方法是向类 Ring 添加另一个成员。喜欢 ringTests :: (Eq a, Arbitrary a) => proxy a -> IO Result .代理参数将是必要的，以便调用者可以指定要测试的类型:ringTests (Proxy :: Proxy Matrix) .
ringTests可以有一个易于编写的默认实现；您可能需要 ScopedTypeVariables获取范围内的类型变量。

您当然也可以将测试函数放在一个单独的类中，同样使用默认实现。那么你只需要写 instance RingTests Matrix where等等，不需要实现。