title: How can I change the directory where cabal stores the documentation
body: <p>I installed a custom Haskell toolchain with the prefix <code>$HOME/usr</code>, so the compiler lives in <code>$HOME/usr/bin/ghc</code> and the documentation in <code>$HOME/usr/share/doc/ghc/...</code>. The toolchain consists of a <code>ghc</code> installation, a <code>cabal</code> installation and all the libs you need. I set up <code>$PATH</code> in a way, that all these programs are in it. There is no other installation of these tools on my system.</p>
  
  <p>Now I tried to install some other libraries. But I always got the same error when cabal tried to install the documentation:</p>
  
  <pre>
  ~$ cabal install --global binary
  Resolving dependencies...
  Configuring binary-0.5.0.2...
  Preprocessing library binary-0.5.0.2...
  Building binary-0.5.0.2...
   ... snip ...
  Registering binary-0.5.0.2...
  cabal: /usr/local/share/doc: permission denied
  </pre>
  
  <p>How can I tell cabal where the documentation should live? I don't want to give this information again and again in the shell, so the best would be a config file. I want to have all the haskell related stuff in my home tree, to avoid destroying my system with a wrong command. </p>