title: How can I uninstall a version of a Cabal package?
body: <p>Happstack Lite is breaking on me because it's getting blaze-html version 0.5 and it wants version 0.4.  Cabal says that <em>both</em> versions 0.4.3.4 and 0.5.0.0 are installed.  I want to remove the 0.5.0.0 and use just the older version.  But cabal does not have an "uninstall" command, and when I try <code>ghc-pkg unregister --force blaze-html</code>, <code>ghc-pkg</code> says my command has been ignored.  </p>
  
  <p>What do I do?</p>
  
  <p><strong>UPDATE</strong>: <em>Don't believe it</em>.  Although <code>ghc-pkg</code> claims to ignore the command, the command <em>isn't</em> ignored.  And with Don Stewart's accepted answer you can remove exactly the version you wish to eliminate.</p>