Haskell RIO monad内部永久存在池

问题描述

相似的问题：Haskell / Persistent-Sqlite: "No instance for (Control.Monad.Trans.Resource.MonadResource IO)"

我正在尝试使用selectSource中的persistent以流模式读取数据库，并使用logInfo在控制台中记录值。

以下片段在RIO项目模板中执行。

以下代码包含有效和无效的部分。

{-# LANGUAGE DerivingStrategies         #-}
{-# LANGUAGE EmptyDataDecls             #-}
{-# LANGUAGE FlexibleContexts           #-}
{-# LANGUAGE GADTs                      #-}
{-# LANGUAGE GeneralizednewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses      #-}
{-# LANGUAGE OverloadedStrings          #-}
{-# LANGUAGE QuasiQuotes                #-}
{-# LANGUAGE StandaloneDeriving         #-}
{-# LANGUAGE TemplateHaskell            #-}
{-# LANGUAGE TypeFamilies               #-}
{-# LANGUAGE UndecidableInstances       #-}
module disambiguate.People where

import           Data.Conduit
import qualified Data.Conduit.List       as CL
import           Database.Persist
import           Database.Persist.sqlite
import           Database.Persist.TH
import           Import                  hiding (on,(^.))
import           Prelude                 (print)

share [mkPersist sqlSettings,mkMigrate "migrateall"] [persistLowerCase|
Person
    name String
    age Int
    deriving Show
|]

disambiguatePeople :: RIO App ()
disambiguatePeople = do
  -- WORKS!
  runsqlite ":memory:" insertAndRead

  -- DOES NOT COMPILE!
  withsqlitePool ":memory:" 1 $ \pool -> do
    liftsqlPersistMPool insertAndRead pool

 where
  insertAndRead = do
    runMigration migrateall

    insert_ $ Person "John Doe" 35
    insert_ $ Person "Jane Doe" 50

    runconduit $ selectSource [PersonAge >. 5] [] .| CL.mapM_
      (lift . logInfo . displayShow)

我收到以下错误：

src/Run.hs:37:25: error:
    • Couldn't match type ‘RIO App’ with ‘IO’
      Expected type: ReaderT
                       sqlBackend
                       (monad-logger-0.3.35:Control.Monad.Logger.NoLoggingT
                          (Control.Monad.Trans.Resource.Internal.ResourceT IO))
                       ()
        Actual type: ReaderT
                       sqlBackend
                       (monad-logger-0.3.35:Control.Monad.Logger.NoLoggingT
                          (Control.Monad.Trans.Resource.Internal.ResourceT (RIO App)))
                       ()
    • In the first argument of ‘liftsqlPersistMPool’,namely
        ‘insertAndRead’
      In a stmt of a 'do' block: liftsqlPersistMPool insertAndRead pool
      In the expression: do liftsqlPersistMPool insertAndRead pool
   |
37 |     liftsqlPersistMPool insertAndRead pool
   |                         ^^^^^^^^^^^^^

由于函数liftsqlPersistMPool对IO类型进行了硬编码，因此我理解该错误。

如何解决此问题以将其与RIO类型一起使用？

解决方法

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