** customizable comment formats
   :PROPERTIES:
   :tangle:   yes
   :comments: yes
   :DATE:     2010-09-05
   :END:

#+begin_src emacs-lisp :results silent
  (setq org-babel-tangle-comment-format-beg "{-# LINE %start-line \"%file\" #-}"
        org-babel-tangle-comment-format-end ""
        org-babel-tangle-pad-newline)
#+end_src

#+begin_src haskell :tangle Main.hs
  test = length
  main = print $ test [1,2,3]
#+end_src

I would like the following output in the tangled file Main.hs:

: {-# LINE 4 "Haskell.org" #-}
: test = length
: main = print $ test [1,2,3]