即使安装了 mtl，也找不到模块“Control.Monad.State”

Question

import Control.Monad.State当我尝试加载包含\n的模块时我得到了

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Could not find module \xe2\x80\x98Control.Monad.State\xe2\x80\x99\nPerhaps you meant\n  Control.Monad.ST (from base-4.8.2.0)\n  Control.Monad.ST.Safe (from base-4.8.2.0)\n  Control.Monad.Fix (from base-4.8.2.0)\nUse -v to see a list of the files searched for.\nFailed, modules loaded: none.\n

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我安装了 Haskell Platform，其中安装了 cabal 和 mtl。

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当我跑步cabal update然后cabal install mtl：

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Resolving dependencies...\nAll the requested packages are already installed:\nmtl-2.2.1\nUse --reinstall if you want to reinstall anyway.\n

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我尝试了重新安装标志，但它只是不断警告我，我将破坏其他软件包，所以我没有继续。

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我的ghc --version是version 7.10.3。cabal --version是1.22.5.0

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这是我跑步时得到的结果ghc-pkg list mtl：

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WARNING: cache is out of date: Library/Frameworks/GHC.framework/Versions/7.10.3-x86_64/usr/lib/ghc-7.10.3/package.conf.d/package.cache\nghc will see an old view of this package db. Use 'ghc-pkg recache' to fix.\n/Library/Frameworks/GHC.framework/Versions/7.10.3-x86_64/usr/lib/ghc-7.10.3/package.conf.d\n   mtl-2.2.1\n

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当我跑时ghc-pkg check：

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WARNING: cache is out of date: /Library/Frameworks/GHC.framework/Versions/7.10.3-x86_64/usr/lib/ghc-7.10.3/package.conf.d/package.cache\nghc will see an old view of this package db. Use 'ghc-pkg recache' to fix.\n

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当我跑的时候ghc-pkg recache

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ghc-pkg: /Library/Frameworks/GHC.framework/Versions/7.10.3-x86_64/usr/lib/ghc-7.10.3/package.conf.d/package.cache: you don't have permission to modify this file\n

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