So I spent a couple hours editing Haskell. So of course I had to spend at least that long customizing emacs. My particular interest is in so called literate haskell code that intersperses LaTeX and Haskell.

The first step is to install haskell-mode and mmm-mode.

apt-get install haskell-mode mmm-mode

Next, add something like the following to your .emacs

(load-library "haskell-site-file")
;; Literate Haskell [requires MMM]
(require 'mmm-auto)
(require 'mmm-haskell)
(setq mmm-global-mode 'maybe)
(add-to-list 'mmm-mode-ext-classes-alist
   '(latex-mode "\\.lhs$" haskell))

Now I want to think about these files as LaTeX with bits of Haskell in them, so I tell auctex that .lhs files belong to it (also in .emacs)

(add-to-list 'auto-mode-alist '("\\.lhs\\'" . latex-mode))
(eval-after-load "tex"
'(progn
    (add-to-list 'LaTeX-command-style '("lhs" "lhslatex"))
    (add-to-list 'TeX-file-extensions "lhs")))

In order that the

 \begin{code}
 \end{code}

environment is typeset nicely, I want any latex file that uses the style lhs to be processed with the script lhslatex (hence the messing with LaTeX-command-style). At the moment I just have an empty lhs.sty, but in principle it could contain useful definitions, e.g. the output from lhs2TeX on a file containing only

%include polycode.fmt

The current version of lhslatex is a bit crude. In particular it assumes you want to run pdflatex.

The upshot is that you can use AUCTeX mode in the LaTeX part of the buffer (i.e. TeX your buffer) and haskell mode in the \begin{code}\end{code} blocks (i.e. evaluate the same buffer as Haskell).