To use haskell-mode in Emacs, add the following lines to your ~/.emacs:

(setq auto-mode-alist
      (append auto-mode-alist
              '(("\\.[hg]s$"  . haskell-mode)
                ("\\.hi$"     . haskell-mode)
                ("\\.l[hg]s$" . literate-haskell-mode))))
(autoload 'haskell-mode "haskell-mode"
   "Major mode for editing Haskell scripts." t)
(autoload 'literate-haskell-mode "haskell-mode"
   "Major mode for editing literate Haskell scripts." t)

Add the following lines according to which modules you want to use:

(add-hook 'haskell-mode-hook 'turn-on-haskell-decl-scan)
(add-hook 'haskell-mode-hook 'turn-on-haskell-doc-mode)
(add-hook 'haskell-mode-hook 'turn-on-haskell-indent)
;(add-hook 'haskell-mode-hook 'turn-on-haskell-simple-indent)
(add-hook 'haskell-mode-hook 'turn-on-font-lock)

Note that the two indentation modules are mutually exclusive - add at
most one.