Question

git url: 'https://github.com/jglick/simple-maven-project-with-tests.git'

在这个haskell程序中，我启用了mpsGeneric开关，该程序的结果是：

{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE QuasiQuotes #-}
module Main
  where

import           Database.Persist.Sql
import           Database.Persist.TH

share
    [mkPersist
        sqlSettings
            { mpsGeneric = True
            , mpsPrefixFields = False
            , mpsEntityJSON = Just EntityJSON
                                { entityToJSON = 'keyValueEntityToJSON
                                , entityFromJSON = 'keyValueEntityFromJSON
                                }
            , mpsGenerateLenses = False
            }
    , mkMigrate "abc"]
    [persistLowerCase|
Test
    a String
|]

main :: IO ()
main = do
    print $ (toSqlKey 1 :: TestId) /= (toSqlKey 1 :: TestId)
    print $ (toSqlKey 1 :: TestId) == (toSqlKey 1 :: TestId)

    print $ (toSqlKey 1 :: TestId) /= (toSqlKey 2 :: TestId)
    print $ (toSqlKey 1 :: TestId) == (toSqlKey 2 :: TestId)

如果禁用mpsGeneric，结果为：

True
True
False
False

看来，上面的Eq实例已被打破。我用

测试程序

True
False
False
True

此＆＃34;功能＆＃34;当我运行以下代码时，我整整一个下午都要杀了我：

persistent of version 2.2.4.1
persistent-template of version 2.1.6

Answer 1

这是一个错误。它现在在github上报告：https://github.com/yesodweb/persistent/issues/560

启用了mpsGeneric的Key的Eq实例看起来很奇怪

1 个答案: