将 Reader monad 与 QuickCheck / monadicIO 结合使用

Question

我想将一个整数作为 CLI 参数传递给使用 QuickCheck / 的 Haskell 程序 monadicIO. 。该整数将在 assert 使测试可定制。问题是，一旦我解析了整数值 main, ，我不知道如何将它传递到内部 monadicIO 调用而不使用像 IORef. 。我认为一个优雅的解决方案可能是 Reader monad，但我找不到让它工作的解决方案，被视为 quickCheck 其论据是僵化的。有任何想法吗？

后来编辑1： 根据要求，我附上了我正在尝试但失败的实际代码。注释掉的行代表我失败的尝试。背景：该测试套件旨在练习一个非常简单的远程端点，该端点计算 QuickCheck 生成的随机输入的 SHA512。远程端点基于 Python/Flask。

稍后编辑2响应@user2407038： 我可以做 propHasExpectedLengthCeiling 接受一个 Int 类型的附加参数，但是 quickCheck 会为其生成随机值，但这不是我想要发生的事情。我的目标是使用 maxSegmentLengthCeiling 我从命令行参数中获取并使用它 let testPassed = actualMaxSegmentLength <= maxSegmentLengthCeiling 里面的 monadicIO 堵塞。现在 maxSegmentLengthCeiling 被指定为顶级值，这意味着每次更改该值时都必须重新编译代码。我还没有任何涉及的代码 IORef 因为这是最后的手段，我的问题的本质是如何避免 IORef 路线。

import qualified Data.ByteString.Lazy.Char8 as LC

import Control.Applicative     ( (<$>) )
import Data.Function           ( on )
import Data.List               ( groupBy )
import Data.Char               ( isDigit )
--import Safe                    ( headMay
--                               , readMay
--                               )
--import System.Environment      ( getArgs )
import Network.HTTP.Conduit    ( simpleHttp )
import Test.QuickCheck         ( Arbitrary
                               , Property
                               , arbitrary
                               , choose
                               , frequency
                               , quickCheckWith
                               , stdArgs
                               , vectorOf
                               )
import Test.QuickCheck.Test    ( Args
                               , maxSuccess
                               )
import Test.QuickCheck.Monadic ( assert
                               , monadicIO
                               , run
                               )

newtype CustomInput = MkCustomInput String deriving Show

instance Arbitrary CustomInput where
  arbitrary =
    let
      genCustomInput = vectorOf 20
                       $ frequency [ (26, choose ('0','9'))
                                   , (10, choose ('a','z'))
                                   ]
    in
      MkCustomInput <$> genCustomInput

maxSegmentLengthCeiling :: Int
maxSegmentLengthCeiling = 22

urlPrefix :: String
urlPrefix = "http://192.168.2.3:5000/sha512sum/"

propHasExpectedLengthCeiling :: CustomInput -> Property
propHasExpectedLengthCeiling (MkCustomInput input) = monadicIO $ do
  testPassed <- run $ do
    response <- simpleHttp $ urlPrefix ++ input
    let stringResponse = LC.unpack response
    let brokenDownStringResponse = groupBy ( (==) `on` isDigit ) stringResponse
    let actualMaxSegmentLength = maximum $ map length brokenDownStringResponse
    let testPassed = actualMaxSegmentLength <= maxSegmentLengthCeiling
    putStrLn ""
    putStrLn ""
    putStrLn $ "Input:       " ++ input
    putStrLn $ "Control sum: " ++ stringResponse
    putStrLn $ "Breakdown:   " ++ show brokenDownStringResponse
    putStrLn $ "Max. length: " ++ show actualMaxSegmentLength
    putStrLn $ "Ceiling:     " ++ show maxSegmentLengthCeiling
    putStrLn $ "Test result: " ++ if testPassed then "Pass" else "Fail"
    putStrLn ""
    putStrLn ""
    return testPassed
  assert $ testPassed

customArgs :: Args
customArgs = stdArgs { maxSuccess = 1000000 }

--readMayAsInt :: String -> Maybe Int
--readMayAsInt = readMay

main :: IO ()
main =
--main = do
--  cliArgs <- getArgs
--  let ceilingInputMay = headMay cliArgs >>= readMayAsInt
--  maxSegmentLengthCeiling <- case ceilingInputMay of
--                               (Just lengthCeiling) -> return lengthCeiling
--                               Nothing              -> error "No valid number given"
  quickCheckWith
    customArgs
    propHasExpectedLengthCeiling

Answer 1

制作 maxSegmentLengthCeiling 一个参数 propHasExpectedLengthCeiling :

propHasExpectedLengthCeiling :: Int -> CustomInput -> Property

并将其调用为

main = do 
  [n] <- getArgs
  quickCheckWith customArgs (propHasExpectedLengthCeiling (read n))