How can I uninstall a version of a Cabal package?

Happstack Lite is breaking on me because it's getting blaze-html version 0.5 and it wants version 0.4. Cabal says that both 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 ghc-pkg unregister --force blaze-html, ghc-pkg says my command has been ignored. What do I do? UPDATE: Don't

[hiratara]

これ、知らなかった。便利だなあ。(dependency hellの底から) 「> cabal sandbox hc-pkg -- unregister」