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Checkers 是一个可重用的QuickCheck属性库,特别是对于标准类型类

如何编写检查器实例来测试我的应用验证实例是否有效？

import Test.QuickCheck
import Test.QuickCheck.Checkers
import Test.QuickCheck.Classes
import Control.Applicative
import Data.Monoid

data Validation e a =
  Error e
  | Scss a
  deriving (Eq, Show)

instance Functor (Validation e) where
  fmap _ (Error e) = Error e
  fmap f (Scss a) = Scss $ f a

instance Monoid e => Applicative (Validation e) where
  pure = Scss
  (<*>) (Scss f) (Scss a) = Scss $ f a
  (<*>) (Error g) (Scss a) = Error g
  (<*>) (Scss a) (Error …