QuickCheck道具到美味道具

Question

我试图从_prop的例子写同样的东西在美味。(来自http://primitive-automaton.logdown.com/posts/142511/tdd-with-quickcheck的例子)

game9_prop :: Game9 -> Bool
game9_prop = (9==) . length . unGame . unGame9

这就是我尝试的美味：

qcTestGengame9 :: TestTree
qcTestGengame9 = QC.testProperty "Better gen rate" $ 
   \ (g :: Game9) -> length . unGame . unGame9 g == 9 --ERROR LINE

此转换将给出以下错误：

test/Tasty.hs:53:11:
Illegal type signature: `Game9'
Perhaps you intended to use -XScopedTypeVariables
In a pattern type-signature

这是Game9类型：

-- To make generation rate better
newtype Game9 = Game9 { unGame9 :: Game }
   deriving (Eq, Show)

instance Arbitrary Game9 where
   arbitrary = (Game9 . Game) `liftM` replicateM 9 arbitrary

Answer 1

若要修复即时错误，请删除类型注释，即使用

qcTestGengame9 :: TestTree
qcTestGengame9 = QC.testProperty "Better gen rate" $ 
   \ g -> (length . unGame . unGame9) g == 9

表达式unGame9 g已经确保了g :: Game9。

但实际上它更简单:使用定义的game9_prop，您可以只使用

qcTestGengame9 :: TestTree
qcTestGengame9 = QC.testProperty "Better gen rate" game9_prop