从stm-conduit粘贴以下代码时：
mygatherFrom :: (MonadIO m, MonadUnliftIO m)
=> Int -- ^ Size of the queue to create
-> (TBQueue o -> m ()) -- ^ Action that generates output values
-> ConduitT () o m ()
mygatherFrom size scatter = do
chan <- liftIO $ newTBQueueIO (fromIntegral size)
worker <- lift $ async (scatter chan)
gather worker chan
where
gather worker chan = do
(xs, mres) <- liftIO $ atomically $ do
xs <- whileM (not <$> isEmptyTBQueue chan) (readTBQueue chan)
(xs,) <$> pollSTM worker
traverse_ yield xs
case mres of
Just (Left e) -> liftIO $ throwIO (e :: SomeException)
Just (Right r) -> return r
Nothing -> gather worker chan
我得到错误：
• Couldn't match type ‘o’ with ‘Element mono0’
‘o’ is a rigid type variable bound by
the type signature for:
mygatherFrom :: forall (m :: * -> *) o.
(MonadIO m, MonadUnliftIO m) =>
Int -> (TBQueue o -> m ()) -> ConduitT () o m ()
at app/Main.hs:(273,1)-(276,32)
Expected type: ConduitT () o m ()
Actual type: ConduitT () (Element mono0) m ()
• In a stmt of a 'do' block: gather worker chan
In the expression:
do chan <- liftIO $ newTBQueueIO (fromIntegral size)
worker <- lift $ async (scatter chan)
gather worker chan
In an equation for ‘mygatherFrom’:
mygatherFrom size scatter
= do chan <- liftIO $ newTBQueueIO (fromIntegral size)
worker <- lift $ async (scatter chan)
gather worker chan
where
gather worker chan
= do (xs, mres) <- liftIO $ atomically $ ...
....
• Relevant bindings include
chan :: TBQueue o (bound at app/Main.hs:278:5)
scatter :: TBQueue o -> m () (bound at app/Main.hs:277:19)
mygatherFrom :: Int -> (TBQueue o -> m ()) -> ConduitT () o m ()
(bound at app/Main.hs:277:1)
我的导入和语言扩展如下：
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE PackageImports #-}
{-# LANGUAGE TupleSections #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE AllowAmbiguousTypes #-}
module Main where
import ClassyPrelude hiding (hClose)
import Conduit
import Control.Concurrent.STM.TBQueue (TBQueue, writeTBQueue)
import qualified Control.Exception.Safe as Ex
import Control.Monad.Catch (MonadMask)
import Control.Monad.Writer
import Data.Bits (shiftR, (.&.))
import qualified Data.ByteString.Char8 as B
import Data.Conduit.Async
import qualified Data.Conduit.List as CL
import Data.Function ((&))
import qualified Data.List as List
import qualified Data.Text as T
import GHC.IO.Handle (Handle, hClose)
import qualified Network.Simple.TCP as TCP
import qualified Network.Socket as NS
import qualified System.IO as IO
import UnliftIO.Concurrent (ThreadId, forkIO, threadDelay)
我觉得我以前见过这类问题，但我不确定是什么导致了冲突。