cabal install HDBC-mysql
But please note...
This page is obsolete! Bryan O'Sullivan has kindly stepped in to continue maintaining this project. See the GitHub project page for current information and details.
If you're interested, you can pull the old repostory via
darcs get http://www.maubi.net/~waterson/REPO/HDBC-mysql
(Note that this repository is a darcs 2.0 repository, and you can't pull it with darcs 1.x.)