错误：“无法加载'Data.Either.Utils'的接口” [英] Error: "Failed to load interface for 'Data.Either.Utils'"

问题描述

有人知道为什么这个特定的导入语句会引起问题吗？我正在使用沙盒和阴谋集团。我的其他导入工作正常（Web.Scotty，Data.Text.Lazy等）。我正在运行 cabal exec runghc filename.hs。我没有cabal.config文件，但是我有cabal.sandbox.config文件。

Does anyone know why this single, specific import statement is causing a problem? I'm using sandbox and cabal. My other imports work fine (Web.Scotty, Data.Text.Lazy, etc.). I'm running with "cabal exec runghc filename.hs". I don't have a cabal.config file, but I do have a cabal.sandbox.config file.

我正在尝试使用forceEither函数，这是在 Data.Either.Utils 中。据我所知，我的导入语句是正常的：

I'm attempting to use the forceEither function, which is in Data.Either.Utils. My import statements are normal as far as I can tell:

{-# LANGUAGE OverloadedStrings #-}
import Web.Scotty
import Control.Monad.Trans (liftIO)
import Data.Aeson (object, (.=))
import Network.HTTP.Types.Status
import Data.Text.Lazy
import Data.Text.Lazy.IO
import Data.Either.Utils

import Data.Monoid (mconcat)

消息：

filename.hs:8:1: error:
    Failed to load interface for ‘Data.Either.Utils’
    Use -v to see a list of the files searched for.

运行-v显示：

Using a sandbox located at
/Users/myuser/Desktop/mydirectory/myotherdirectory/.cabal-sandbox
/usr/local/bin/ghc --print-global-package-db
/usr/local/bin/runghc filename.hs

推荐答案

Data.Either.Utils 模块不属于基础 Haskell；它是MissingH软件包的一部分，而该软件包似乎是..哈哈..丢失！

The Data.Either.Utils module is not part of "base" Haskell; it's part of the MissingH package, and that package seems to be .. ha ha .. missing!

我对Cabal沙箱不太熟悉（我使用Stack） ，但大概可以运行：

I'm not too familiar with Cabal sandboxes (I use Stack), but presumably you can run:

cabal install MissingH

在沙箱中，您应该会很好。

in your sandbox, and you should be good to go.

如果这不起作用，只需复制来自MissingH的 forceEither 的代码：

If that doesn't work, just copy the code for forceEither from MissingH:

forceEither :: Show e => Either e a -> a
forceEither (Left x) = error (show x)
forceEither (Right x) = x

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