# Haskell Mode for Emacs: Installation Guide

When Emacs is started up, it normally runs a file called `~/.emacs` located in your home directory. This file should contain all of your personal customisations written as a series of Elisp commands. In order to install the Haskell mode, you have to tell Emacs where to find it. This is done by adding some commands to the init file.

## Installation

- If you are using XEmacs, the haskell-mode package should be available for installation through the XEmacs package UI.
- If you are using Debian, you can install the package haskell-mode with a command like "apt-get install haskell-mode".

Otherwise:

- Download and unpack the basic mode and modules into a suitable directory, e.g. `~/lib/emacs` where `~` stands for your home directory.

- Assuming you have placed the basic mode `haskell-mode.el` and the modules you want to use in the directory `~/lib/emacs`, add the following command to your init file (`~/.emacs`):

      (load "~/lib/emacs/haskell-site-file")

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

      (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)

  Note that the two indentation modules are mutually exclusive - add at most one. Note that the line of code for simple indentation is commented out (using a preceeding `;`) in preference for the more advanced indentation module. Installation is now complete!

  The other modules are automatically loaded when needed in the following way:

  - Font locking: just turn it on via `global-font-lock-mode` or do

        (add-hook 'haskell-mode-hook 'font-lock-mode)

  - Declaration scanning: just use `M-x imenu` or bind `imenu` to a key. E.g.

        (global-set-key [(control meta down-mouse-3)] 'imenu)

    or you can also add it to the menubar with

        (add-hook 'haskell-mode-hook 'imenu-add-menubar-index)

  - Interaction with inferior Haskell interpreter: just hit `C-c C-z` or `C-c C-l`.

For those interested, each command above shall now be explained.

1. We must ensure that the directory containing `haskell-mode.el` is on the `load-path` of Emacs. You can examine the value of the `load-path` by typing `C-h v load-path` in an Emacs session. Supposing that you've placed `haskell-mode.el` in the directory `~/lib/emacs`, if this directory is not on the `load-path` we add it with:

       (setq load-path (cons "~/lib/emacs" load-path))

   The function `setq` sets the value of a variable, and the function `cons` takes an element and a list and creates a new list with the former as head and the latter as tail, as in Haskell.

2. It is possible (and desirable) for Emacs to enter a specific mode according to the name of the file being edited/visited. The variable `auto-mode-alist` tells Emacs what mode to run according to which regular expression matches the filename. We wish to run the Haskell mode on all files ending in `.hs`, `.hi` (interface file) and `.gs` (Gofer file), and to run the Haskell mode for literate scripts on all files ending in `.lhs` and `.lgs`. To do this, we need to add pairs of the form `(regexp . mode-function)`. We use the function `append` to append a list of three such pairs to the end of the value of `auto-mode-alist`. A list in Elisp is written within round parantheses with elements separated by whitespace. A list is treated as a function application unless it is quoted with `'`, which is what we do.

3. In order for Emacs to know where to find the definition of our mode functions, `haskell-mode` and `literate-haskell-mode`, we must use the function `autoload`. Both mode functions can be found in the file `haskell-mode.el` which was downloaded in the first installation step (the `.el` extension is left off and assumed by Emacs). As we have already ensured that this file is on the `load-path` we need only give the filename and not the directory. Its use is quite straightforward but for further information, see its documentation by entering `C-h f autoload` in an Emacs session.

4. Each function `turn-on-haskell-module` turns on the corresponding module. Adding such a function as a hook to the Haskell mode will turn on that module when the mode is used. Note that each of these modules may slow down Emacs, especially for large files.

## Customisation

Most customisations are on the functionality of a particular module. See the documentation of that module for information on its customisation.

## Support

Any problems, do mail and we will try our best to help you!

Haskell Mode Home Page.