This is part of the Emacs Starter Kit.
Support for editing Haskellpretty lambdas in Haskell code
(defun pretty-lambdas-haskell ()
(font-lock-add-keywords
nil `((,(concat "(?\\(" (regexp-quote "\\") "\\)")
(0 (progn (compose-region (match-beginning 1) (match-end 1)
,(make-char 'greek-iso8859-7 107))
nil))))))
Haskell mode hook
(add-hook 'haskell-mode-hook 'run-coding-hook)
(add-hook 'haskell-mode-hook 'pretty-lambdas-haskell)