如何使用data.validation撰写错误

Question

我正在使用精彩的Data.Validation包进行验证。但是，我无法为复杂类型正确地编写它们。

我分别为电子邮件和密码Email和密码创建了类型。我已经创建了可以使用Data.Validation包累积的验证和错误。我做了一个名为data Creds = Email Password的新类型。现在，我无法从电子邮件和密码中累积错误

`

``
{-# LANGUAGE OverloadedStrings   #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE DeriveGeneric       #-}

module ErrorComposition
  ()
where


import           Data.Text                     as T
import           Data.Validation
import           Control.Lens


------------------------------------
-- validations and errors for Email
------------------------------------
data Email =  Email
  {
    email :: Text
  } deriving (Show)

data EmailError = EmailNoDotError | EmailNoPeriodError
  deriving (Show)


noDot :: Email -> Validation [EmailError] ()
noDot x = if "." `isInfixOf` (email x)
  then _Success # ()
  else _Failure # [EmailNoDotError]

noPeriod :: Email -> Validation [EmailError] ()
noPeriod x = if "@" `isInfixOf` (email x)
  then _Success # ()
  else _Failure # [EmailNoPeriodError]

validateEmail :: Email -> Validation [EmailError] ()
validateEmail e = noDot e <* noPeriod e

mkEmail :: Text -> Validation [EmailError] Email
mkEmail e = pure (Email e) <* validateEmail (Email e)



-----------------------------------------------------------
-- validations for password and errors
-- --------------------------------------------------------

data Password = Password
  {
    password :: Text
  } deriving Show

data PasswordError = MinLengthPasswordError | NotStrongPasswordError
 deriving (Show)

minLength :: Int -> Password -> Validation [PasswordError] ()
minLength n x | T.length (password x) >= n = _Success # ()
              | otherwise                  = _Failure # [MinLengthPasswordError]

notStrong :: Password -> Validation [PasswordError] ()
notStrong x = if "strong" `isInfixOf` (password x)
  then _Success # ()
  else _Failure # [NotStrongPasswordError]

validatePassword :: Password -> Validation [PasswordError] ()
validatePassword p = minLength 7 p <* notStrong p

mkPassword :: Text -> Validation [PasswordError] Password
mkPassword p = pure (Password p) <* validatePassword (Password p)



--------------------------------------------------------------------
-- Domain Modelling for an Creds type
-- The expectation is errors from email and password should be combined
-- ----------------------------------------------------------------

data Creds = Creds
  {
    credsEmail :: Email
  , credsPassword:: Password
  } deriving (Show)

data CredsError = EmailError | PasswordError
 deriving (Show)

validateCreds :: Creds -> Validation [CredsError] ()
--validateCreds (Creds e p) = validateEmail e <* validatePassword p
validateCreds = undefined

mkCreds :: Email -> Password -> Validation [CredsError] Creds
mkCreds e p = pure (Creds e p) <* validateCreds (Creds e p)

ErrorComposition> let e1= mkEmail "bob"
*ErrorComposition> show e1
"Failure [EmailNoDotError,EmailNoPeriodError]"
*ErrorComposition> let p1 = mkPassword "he"
*ErrorComposition> show p1
"Failure [MinLengthPasswordError,NotStrongPasswordError]"
*ErrorComposition> let c1 = mkCreds (Email "bob") (Password "he")



What Am I expecting? 
Failure [EmailNoDotError, EmailNoPeriodError, MinLengthPasswordError,NotStrongPasswordError] 

1. Is it possible to get the above result?
2. Even if the above result is not possible because the error types differ, atleast, I'm looking for a way to get the following:
  Failure ["EmailNoDotError", "EmailNoPeriodError", 
           "MinLengthPasswordError,"NotStrongPasswordError"] 
3. Essentially could you please help me in fixing the validateCreds function above in the code?

Answer 1

我将使用Either EmailError PasswordError作为组合类型。您可以改为创建自定义和类型。

mkCreds :: Text -> Text -> Validation [Either EmailError PasswordError] Creds
mkCreds e p = Creds <$> first Left (mkEmail e) <*> first Right (mkPassword p)

这有三件事：

• 使用mkEmail和mkPassword来验证每个部分
• 使用Either和first Left将错误提升到first Right错误类型
• 将所有错误或Creds的所有部分与<$>和<*>结合起来