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Emacs/Literate programming

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Literate programming

1 Literate Haskell

Literate Haskell is supported directly by haskell-mode without having to use MMM or other tricks that may be found in old mailing list postings, so ignore that out of date information. If you load an .lhs file, then literate haskell should automatically work. If it doesn't then you should make sure that you are using a current version of haskell-mode and that the correct literate type is selected. You can switch between bird (the default) and tex by typing:

M-x customize-variable RET haskell-literate-default

2 Multiple modes

Another useful tool for literate programmers is the mmm-mode for Emacs. mmm-mode switches the current major mode of the buffer between two alternatives, depending on the context the cursor is in. If you're in, say, a \begin{code}...\end{code} block, you'll be editing in haskell-mode, but once you leave that block, you'll be editing in latex-mode.

I have managed to cook up a configuration for both literate styles, but surely some Emacs guru can enhance these. To configure mmm-mode for Haskell, add these lines to your .emacs file:

(add-hook 'haskell-mode-hook 'my-mmm-mode)

    :submode text-mode
    :front "^[^>]"
    :include-front true
    :back "^>\\|$"
    :submode literate-haskell-mode
    :front "^\\\\begin{code}"
    :front-offset (end-of-line 1)
    :back "^\\\\end{code}"
    :include-back nil
    :back-offset (beginning-of-line -1)

(defun my-mmm-mode ()
  ;; go into mmm minor mode when class is given
  (make-local-variable 'mmm-global-mode)
  (setq mmm-global-mode 'true))

(setq mmm-submode-decoration-level 0)

You can activate mmm-mode by running "M-x mmm-ify-by-class" in the buffer. Emacs will prompt you for the class to use, to which should answer literate-haskell-bird or literate-haskell-latex, respectively.

If you want Emacs to activate mmm-mode automatically for certain literate Haskell files, add these lines to it at the end:

% ----- Configure Emacs -----
% Local Variables: ***
% mode: latex ***
% mmm-classes: literate-haskell-latex ***
% End: ***

This is, what the my-mmm-mode hook does, by the way.