当尝试在其他计算机上重现此问题时，每5台计算机中只有2台出现此问题.在它们两个上，我都以相同的方式和顺序安装了cabal软件包.

When trying to reproduce this issue on other computers, only 2 out of 5 computers had this issue. On both of them I installed cabal packages in about the same way and order.

回想一下，我认为这个问题是由于某些破损的包装造成了严重破坏而引起的:

In retrospect I assume this issue arose because of some broken packages wreaking havoc:

$ ghc-pkg check
There are problems in package feed-0.3.9.2:
  dependency "xml-1.3.13-dd52b1688e97a3c6cd0aa48dba7b153e" doesn't exist
There are problems in package hxt-9.3.1.3:
  dependency "network-2.4.2.2-ea77cdf1bc747bc58308fdeb52745c4d" doesn't exist
There are problems in package hspec-1.8.1.1:
  dependency "QuickCheck-2.6-409fcc32c191cd6e04afdebb15869820" doesn't exist
There are problems in package quickcheck-io-0.1.0:
  dependency "QuickCheck-2.6-409fcc32c191cd6e04afdebb15869820" doesn't exist
There are problems in package regex-compat-0.95.1:
  dependency "regex-base-0.93.2-2023953b859e6f91efe89733d2ef5421" doesn't exist
There are problems in package regex-posix-0.95.2:
  dependency "regex-base-0.93.2-2023953b859e6f91efe89733d2ef5421" doesn't exist
There are problems in package hxt-9.3.1.2:
  dependency "network-2.4.2.2-ea77cdf1bc747bc58308fdeb52745c4d" doesn't exist

The following packages are broken, either because they have a problem
listed above, or because they depend on a broken package.
feed-0.3.9.2
hxt-9.3.1.3
hspec-1.8.1.1
quickcheck-io-0.1.0
regex-compat-0.95.1
regex-posix-0.95.2
hxt-9.3.1.2
MissingH-1.2.0.2
yesod-test-1.2.1

请注意，没有列出 pandoc 和 yaml (我在问了问题后就安装了它，并且与 pandoc 完全一样)在那里.

Note that neither pandoc nor yaml (I installed it after asking the question and had the exact same issues as with pandoc) are listed there.

对于也有类似问题的用户，请确保:

For users also having a similar problem, please ensure:

1. 该软件包已安装，并且您不在任何未安装该软件包的沙箱中.

1. The package is installed and you're not inside any sandbox where the package is not installed.

在执行测试脚本的目录中，确保没有 Text/Pandoc 文件夹(或等效文件夹，具体取决于引起问题的程序包)

In the directory where you're executing the test script, ensure that there is no Text/Pandoc folder (or equivalent, depending on the package causing the problem

使用 runghc -v 运行测试脚本以检查其是否搜索正确的目录

Run your test script with runghc -v to check if it searches the proper directory

ghc-pkg list 列出已安装的软件包，并且没有软件包损坏(使用 ghc-pkg check 进行检查)

ghc-pkg list lists your package as installed, and no packages are broken (use ghc-pkg check to check)

我通过重命名〜/.cabal 和〜/.ghc 解决了我的问题.请注意，我这样做时缺少 proper 解决方案，我认为您应该只在万不得已时才这样做.

I solved my problem by renaming ~/.cabal and ~/.ghc. Note that I did this lacking a proper solution, I think you should only do this as a last resort.