无法将类型Data.Enumerator.Internal.Iteratee与IO匹配

Question

import qualified Data.ByteString.Lazy as L
import Data.Enumerator.List (consume)

data App = App
mkYesod "App" [parseRoutesNoCheck|
/*Texts WikR GET --PathMultiPiece handler for all combinations
/ WikiR POST
|]
instance Yesod App

getWikR :: [Text] -> Handler Text
getWikR parts = return "" --defaultLayout [whamlet||]

postWikiR = do
    bss <- lift consume
    return $ RepJson $ toContent $ L.fromChunks bss

main :: IO ()
main = warp 3000 App

给出错误，

yesod/hw.hs:14:1:
    Couldn't match type ‘Data.Enumerator.Internal.Iteratee
                           Data.ByteString.Internal.ByteString m0’
                  with ‘IO’
    Expected type: HandlerT App IO RepJson
      Actual type: HandlerT
                     App
                     (Data.Enumerator.Internal.Iteratee
                        Data.ByteString.Internal.ByteString m0)
                     RepJson
    In the first argument of ‘yesodRunner’, namely ‘postWikiR’
    In the expression:
      yesodRunner postWikiR env3739_adGV (Just WikiR) req3739_adGW

错误行@ ln-num＃14为mkYesod "App" [parseRoutesNoCheck|

我确信，错误与postWikiR#return $ RepJson $ toContent $ L.fromChunks bss有关。但不确定，如何解决？

Reference-1

Answer 1

可能您正在尝试运行与当前Yesod不兼容的旧代码。

您可以使用

编译并运行（ghc-7.10.1，yesod-1.4.1.5）

import Data.Enumerator (run_)
...
bss <- run_ consume

但我不确定你想要它做什么。按原样，它将返回一个空列表。