haskell - GHC 包被隐藏

Question

我正在尝试运行这个从 Haskell wiki 获得的简单示例.

import GHC
import GHC.Paths ( libdir )
import DynFlags

main = 
    defaultErrorHandler defaultFatalMessager defaultFlushOut $ do
      runGhc (Just libdir) $ do
        dflags <- getSessionDynFlags
        setSessionDynFlags dflags
        target <- guessTarget "test_main.hs" Nothing
        setTargets [target]
        load LoadAllTargets

我收到的错误消息是:

amy@wombat$ ghc --make amy15.hs 

amy15.hs:1:8:
    Could not find module ‘GHC’
    It is a member of the hidden package ‘ghc-7.8.3’.
    Use -v to see a list of the files searched for.

amy15.hs:3:8:
    Could not find module ‘DynFlags’
    It is a member of the hidden package ‘ghc-7.8.3’.
    Use -v to see a list of the files searched for.

现在，我正在使用 ghc-7.8.3 进行编译，因此显然该软件包已安装。

amy@wombat$ cabal info ghc
* ghc              (library)
    Versions available: [ Not available from server ]
    Versions installed: 7.8.3
... and so on

为什么 GHC 无法看到 ghc 包？

Answer 1

显然 ghc 包默认是隐藏的，至少如果你像我一样手动安装 ghc，而不是安装 Haskell 平台。所以我需要“取消隐藏”该包，如下所示:

sudo ghc-pkg expose ghc