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我对 Haskell 很陌生，我正在尝试跟随Happstack Crash Course。我已经完成了一些示例，但是当我尝试happstack-heist 示例时，我得到了一个奇怪的编译错误。我正在编译的文件如下所示：

module Main where

import Control.Applicative    ((<$>))
import Control.Monad          (msum)
import qualified Data.Text    as T
import Happstack.Server       ( dir, nullConf, nullDir, simpleHTTP
                              , seeOther, toResponse
                              )
import Happstack.Server.Heist (heistServe, initHeistCompiled)
import Heist                  (Splices, (##), getParamNode, noSplices)
import Heist.Compiled         (Splice, yieldRuntimeText)
import qualified Text.XmlHtml as X

-- | factorial splice
factSplice :: (Monad m) => Splice m
factSplice = do
  intStr <- T.unpack . X.nodeText <$> getParamNode
  let res = yieldRuntimeText $ do
        case reads intStr of
          [(n,[])] ->
            return (T.pack $ show $ product [1..(n :: Integer)])
          _ ->
            return (T.pack $ "Unable to parse " ++
                    intStr ++ " as an Integer.")
  return $ res

main :: IO ()
main = do
  heistState <- do
    r <- initHeistCompiled (T.pack "fact" ## factSplice) noSplices "."
    case r of
      (Left e) -> error $ unlines e
      (Right heistState) -> return $ heistState
  simpleHTTP nullConf $ msum
    [ dir "heist" $ heistServe heistState
    , nullDir >>
      seeOther "/heist/factorial" (toResponse "/heist/factorial")
    ]

错误是：

test.hs:37:36:
    Couldn't match expected type `happstack-server-7.3.9:Happstack.Server.Internal.Types.Response'
                with actual type `Happstack.Server.Internal.Types.Response'
    In the return type of a call of `toResponse'
    In the second argument of `seeOther', namely
      `(toResponse "/heist/factorial")'
    In the second argument of `(>>)', namely
      `seeOther "/heist/factorial" (toResponse "/heist/factorial")'

似乎有些东西想要以包名称和版本号为前缀的类型，我不明白。happstack-server 和 happstack-heist 都安装了cabal install.

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1 回答 1

3

欢迎来到阴谋集团地狱！发生的情况是，当您为此示例安装了两个软件包时happstack-server，happstack-heist其中一个与您的系统上已安装的版本不同。当您尝试编译示例时，编译器无法确定使用哪一个。解决方案是沙盒。只是cd到你有这个例子的目录，运行cabal sandbox init，然后cabal install --dependencies-only。这将使用.cabal文件获取项目的所有依赖项并将它们安装在本地.cabal-sandbox/目录中。当您运行cabal build或cabal install从该本地文件夹中提取依赖项时，任何可执行文件都将安装在.cabal-sandbox/bin.

于 2015-01-19T21:53:00.627 回答