Haskell-mode is a major Emacs mode for editing Haskell source code. It
provides syntax highlighting and automatic indentation and comes with
inf-haskell which allows interaction with an inferior Haskell interactive
loop such as the one of Hugs or GHCi.

Note that if you want to use haskell-mode under XEmacs, you should
install editors/xemacs-packages instead.

WWW: http://projects.haskell.org/haskellmode-emacs/