emacs/init.org

#+LATEX_HEADER: \usepackage{parskip}
#+LATEX_HEADER: \usepackage{inconsolata}
#+TITLE: Emacs configuration file
#+AUTHOR: Lars Tveito

* About
  This is a Emacs configuration file written in =org-mode=. There are a few
  reasons why I wanted to do this. My =.emacs.d/= was a mess, and needed a
  proper clean-up. Also I like keeping all my configurations in a single
  file, using =org-mode= I can keep this file /organized/. I aim to briefly
  explain all my configurations.

* Configurations
** Meta

   Emacs can only load =.el=-files. We can use =C-c C-v t= to run
 =org-babel-tangle=, which extracts the code blocks from the current file
   into a source-specific file (in this case a =.el=-file).

   To avoid doing this each time a change is made we can add a function to
   the =after-save-hook= ensuring to always tangle and byte-compile the
 =org=-document after changes.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defun init-hook ()
       "If the current buffer is 'init.org' the code-blocks are
     tangled, and the tangled file is compiled."
       (when (equal (buffer-file-name)
                    (expand-file-name (concat user-emacs-directory "init.org")))
         (org-babel-tangle)
         (byte-compile-file (concat user-emacs-directory "init.el"))))

     (add-hook 'after-save-hook 'init-hook)
   #+END_SRC

** Package

   Managing extensions for Emacs is simplified using =package= which
   is built in to Emacs 24 and newer. To load downloaded packages we
   need to initialize =package=.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (require 'package)
     (package-initialize)
   #+END_SRC

   Packages can be fetched from different mirrors, [[http://melpa.milkbox.net/#/][melpa]] is the largest
   archive and is well maintained.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (add-to-list 'package-archives
                  '("MELPA" . "http://melpa.milkbox.net/packages/") t)
   #+END_SRC

   We can define a predicate that tells us wither or not the newest version
   of a package is installed.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defun newest-package-installed-p (package)
       "Return true if the newest available PACKAGE is installed."
       (when (package-installed-p package)
         (let* ((local-pkg-desc (or (assq package package-alist)
                                    (assq package package--builtins)))
                (newest-pkg-desc (assq package package-archive-contents)))
           (version-list-= (package-desc-vers (cdr local-pkg-desc))
                           (package-desc-vers (cdr newest-pkg-desc))))))
   #+END_SRC

   Let's write a function to install a package if it is not installed or
   upgrades it if a new version has been released. Here our predicate comes
   in handy.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defun upgrade-or-install-package (package)
       "Unless the newest available version of PACKAGE is installed
     PACKAGE is installed and the current version is deleted."
       (unless (newest-package-installed-p package)
         (let ((pkg-desc (assq package package-alist)))
           (when pkg-desc
             (package-delete (symbol-name package)
                             (package-version-join
                              (package-desc-vers (cdr pkg-desc)))))
           (package-install package))))
   #+END_SRC

   The =package-refresh-contents= function downloads archive descriptions,
   this is a major bottleneck in this configuration. To avoid this we can
   try to only check for updates once every day or so. Here are to
   variables. The first specifies how often we should check for updates. The
   second specifies wither one should update during the initialization.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defvar days-between-updates 1)
     (defvar do-package-update-on-init t)
   #+END_SRC

<<<<<<< HEAD
   The tricky part is figuring out when the last time the Emacs was updated!
   Here is a hacky way of doing it, using [[http://www.gnu.org/software/emacs/manual/html_node/emacs/Time-Stamps.html][time-stamps]]. By adding a
   time-stamp to the init file, we can search for it and determine wither or
   not to do an update. After that we must run the =time-stamp=-function to
   update the time-stamp. Note that if there is no time-stamp in the
   init-file then packages will be updated every time you start Emacs.
=======
   The tricky part is figuring out when the last time the Emacs was opened!
   Here is a hacky way of doing it, using [[http://www.gnu.org/software/emacs/manual/html_node/emacs/Time-Stamps.html][time-stamps]]. By adding a
   time-stamp to the init file, we can search for it and determine wither or
   not to do an update. After that we must run the =time-stamp=-function to
   update the time-stamp.
>>>>>>> 4bf07b95098fd9e26f03b2217dc256200c136488

   #+BEGIN_SRC emacs-lisp :tangle yes
     (require 'time-stamp)
     ;; Open the 'user-init-file' and write any changes.
     (with-temp-file user-init-file
       ;; Insert it's original content's.
       (insert-file-contents user-init-file)
       (forward-line time-stamp-line-limit)
       (let ((bound (point)))
         (goto-char (point-min))
         ;; We search for the time-stamp.
         (let ((start (re-search-forward time-stamp-start bound t))
               (end (re-search-forward time-stamp-end bound t)))
           (when (and start end)
             ;; Assuming we have found a time-stamp, we check determine if it's
             ;; time to update.
             (setq do-package-update-on-init
                   (<= days-between-updates
                       (days-between
                        (current-time-string)
<<<<<<< HEAD
                        (buffer-substring-no-properties start end))))
             ;; Remember to update the time-stamp.
             (when do-package-update-on-init
               (time-stamp))))))
=======
                        (buffer-substring-no-properties start end)))))))
       ;; Remember to update the time-stamp.
       (time-stamp))
>>>>>>> 4bf07b95098fd9e26f03b2217dc256200c136488
   #+END_SRC

   Now we can use the function above to make sure packages are installed and
   up to date. Here are some packages I find useful (some of these
   configurations are also dependent on them).

   #+BEGIN_SRC emacs-lisp :tangle yes
     (when do-package-update-on-init
       (package-refresh-contents))

     (dolist (package
              '(ac-geiser         ; Auto-complete backend for geiser
                ac-slime          ; An auto-complete source using slime completions
                ace-jump-mode     ; quick cursor location minor mode
                auto-compile      ; automatically compile Emacs Lisp libraries
                auto-complete     ; auto completion
                elscreen          ; window session manager
                expand-region     ; Increase selected region by semantic units
                flx-ido           ; flx integration for ido
                ido-vertical-mode ; Makes ido-mode display vertically.
                geiser            ; GNU Emacs and Scheme talk to each other
                haskell-mode      ; A Haskell editing mode
                jedi              ; Python auto-completion for Emacs
                magit             ; control Git from Emacs
                markdown-mode     ; Emacs Major mode for Markdown-formatted files.
                monokai-theme     ; A fruity color theme for Emacs.
                move-text         ; Move current line or region with M-up or M-down
                multiple-cursors  ; Multiple cursors for Emacs.
                org               ; Outline-based notes management and organizer
                paredit           ; minor mode for editing parentheses
                pretty-lambdada   ; the word `lambda' as the Greek letter.
                smex              ; M-x interface with Ido-style fuzzy matching.
                ))
       (when do-package-update-on-init
         (upgrade-or-install-package package)))
   #+END_SRC

** Require

   Some features are not loaded by default to minimize initialization time,
   so they have to be required (or loaded, if you will).

   #+BEGIN_SRC emacs-lisp :tangle yes
     (dolist (feature
              '(auto-compile             ; auto-compile .el files
                auto-complete-config     ; a configuration for auto-complete-mode
                jedi                     ; auto-completion for python
                pretty-lambdada          ; show 'lambda' as the greek letter.
                ox-latex                 ; the latex-exporter (from org)
                recentf                  ; recently opened files
                tex-mode                 ; TeX, LaTeX, and SliTeX mode commands
                ))
       (require feature))
   #+END_SRC

** Sane defaults

   These are what /I/ consider to be saner defaults.

   We can set variables to whatever value we'd like using =setq=.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (setq initial-scratch-message nil     ; Clean scratch buffer.
           inhibit-startup-message t       ; No splash screen please.
           default-input-method "TeX"      ; Use TeX when toggeling input method.
           ring-bell-function 'ignore      ; Quite as a mouse.
           doc-view-continuous t           ; At page edge goto next/previous.
           echo-keystrokes 0.1             ; Show keystrokes asap.
           )

     ;; Some mac-bindings interfere with Emacs bindings.
     (when (boundp 'mac-pass-command-to-system)
       (setq mac-pass-command-to-system nil))

   #+END_SRC

   Some variables are buffer-local, so changing them using =setq= will only
   change them in a single buffer. Using =setq-default= we change the
   buffer-local variable's default value.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (setq-default fill-column 76                   ; Maximum line width.
                   indent-tabs-mode nil             ; Use spaces instead of tabs.
                   split-width-threshold 100        ; Split verticly by default.
                   auto-fill-function 'do-auto-fill ; Auto-fill-mode everywhere.
                   )
   #+END_SRC

   The =load-path= specifies where Emacs should look for =.el=-files (or
   Emacs lisp files). I have a directory called =site-lisp= where I keep all
   extensions that have been installed manually (these are mostly my own
   projects).

   #+BEGIN_SRC emacs-lisp :tangle yes
     (let ((default-directory (concat user-emacs-directory "site-lisp/")))
       (when (file-exists-p default-directory)
         (normal-top-level-add-to-load-path '("."))
         (normal-top-level-add-subdirs-to-load-path)))
   #+END_SRC

   Answering /yes/ and /no/ to each question from Emacs can be tedious, a
   single /y/ or /n/ will suffice.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (fset 'yes-or-no-p 'y-or-n-p)
   #+END_SRC

   To avoid file system clutter we put all auto saved files in a single
   directory.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defvar emacs-autosave-directory
       (concat user-emacs-directory "autosaves/")
       "This variable dictates where to put auto saves. It is set to a
       directory called autosaves located wherever your .emacs.d/ is
       located.")

     ;; Sets all files to be backed up and auto saved in a single directory.
     (setq backup-directory-alist
           `((".*" . ,emacs-autosave-directory))
           auto-save-file-name-transforms
           `((".*" ,emacs-autosave-directory t)))
   #+END_SRC

   Set =utf-8= as preferred coding system.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (set-language-environment "UTF-8")
   #+END_SRC

   By default the =narrow-to-region= command is disabled and issues a
   warning, because it might confuse new users. I find it useful sometimes,
   and don't want to be warned.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (put 'narrow-to-region 'disabled nil)
   #+END_SRC

   Call =auto-complete= default configuration, which enables =auto-complete=
   globally.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (ac-config-default)
   #+END_SRC

   Automaticly revert =doc-view=-buffers when the file changes on disk.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (add-hook 'doc-view-mode-hook 'auto-revert-mode)
   #+END_SRC

** Modes

   There are some modes that are enabled by default that I don't find
   particularly useful. We create a list of these modes, and disable all of
   these.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (dolist (mode
              '(tool-bar-mode                ; No toolbars, more room for text.
                scroll-bar-mode              ; No scroll bars either.
                blink-cursor-mode            ; The blinking cursor gets old.
                ))
       (funcall mode 0))
   #+END_SRC

   Let's apply the same technique for enabling modes that are disabled by
   default.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (dolist (mode
              '(abbrev-mode                ; E.g. sopl -> System.out.println.
                auto-compile-on-load-mode  ; Compile .el files on load ...
                auto-compile-on-save-mode  ; ... and save.
                column-number-mode         ; Show column number in mode line.
                delete-selection-mode      ; Replace selected text.
                recentf-mode               ; Recently opened files.
                show-paren-mode            ; Highlight matching parentheses.
                ))
       (funcall mode 1))
   #+END_SRC

   This makes =.md=-files open in =markdown-mode=.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (add-to-list 'auto-mode-alist '("\\.md\\'" . markdown-mode))
   #+END_SRC

** Visual

   Change the color-theme to =monokai= (downloaded using =package=).

   #+BEGIN_SRC emacs-lisp :tangle yes
     (load-theme 'monokai t)
   #+END_SRC

   Use the [[http://www.levien.com/type/myfonts/inconsolata.html][Inconsolata]] font if it's installed on the system.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (when (member "Inconsolata" (font-family-list))
       (set-face-attribute 'default nil :font "Inconsolata-13"))
   #+END_SRC

** Ido

   Interactive do (or =ido-mode=) changes the way you switch buffers and
   open files/directories. Instead of writing complete file paths and buffer
   names you can write a part of it and select one from a list of
   possibilities. Using =ido-vertical-mode= changes the way possibilities
   are displayed, and =flx-ido-mode= enables fuzzy matching.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (dolist (mode
              '(ido-mode                   ; Interactivly do.
                ido-everywhere             ; Use Ido for all buffer/file reading.
                ido-vertical-mode          ; Makes ido-mode display vertically.
                flx-ido-mode               ; Toggle flx ido mode.
                ))
       (funcall mode 1))
   #+END_SRC

   We can set the order of file selections in =ido=. I prioritize source
   files along with =org=- and =tex=-files.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (setq ido-file-extensions-order
           '(".el" ".scm" ".lisp" ".java" ".c" ".h" ".org" ".tex"))
   #+END_SRC

   Sometimes when using =ido-switch-buffer= the =*Messages*= buffer get in
   the way, so we set it to be ignored (it can be accessed using =C-h e=, so
   there is really no need for it in the buffer list).

   #+BEGIN_SRC emacs-lisp :tangle yes
     (add-to-list 'ido-ignore-buffers "*Messages*")
   #+END_SRC

   To make =M-x= behave more like =ido-mode= we can use the =smex=
   package. It needs to be initialized, and we can replace the binding to
   the standard =execute-extended-command= with =smex=.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (smex-initialize)
     (global-set-key (kbd "M-x") 'smex)
   #+END_SRC

** Calendar

   Define a function to display week numbers in =calender-mode=. The snippet
   is from [[http://www.emacswiki.org/emacs/CalendarWeekNumbers][EmacsWiki]].

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defun calendar-show-week (arg)
       "Displaying week number in calendar-mode."
       (interactive "P")
       (copy-face font-lock-constant-face 'calendar-iso-week-face)
       (set-face-attribute
        'calendar-iso-week-face nil :height 0.7)
       (setq calendar-intermonth-text
             (and arg
                  '(propertize
                    (format
                     "%2d"
                     (car (calendar-iso-from-absolute
                           (calendar-absolute-from-gregorian
                            (list month day year)))))
                    'font-lock-face 'calendar-iso-week-face))))
   #+END_SRC

   Evaluate the =toggle-calendar-show-week= function.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (calendar-show-week t)
   #+END_SRC

   Set Monday as the first day of the week, and set my location.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (setq calendar-week-start-day 1
           calendar-latitude 60.0
           calendar-longitude 10.7
           calendar-location-name "Oslo, Norway")
   #+END_SRC

** Mail

   I use [[http://www.djcbsoftware.nl/code/mu/mu4e.html][mu4e]] (which is a part of [[http://www.djcbsoftware.nl/code/mu/][mu]]) along with [[http://docs.offlineimap.org/en/latest/][offlineimap]] on one of my
   computers. Because the mail-setup wont work without these programs
   installed we bind =load-mail-setup= to =nil=. If the value is changed to
   a =non-nil= value mail is setup.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defvar load-mail-setup nil)

     (when load-mail-setup
       ;; We need mu4e
       (require 'mu4e)

       ;; Some basic mu4e settings.
       (setq mu4e-maildir           "~/.ifimail"     ; top-level Maildir
             mu4e-sent-folder       "/INBOX.Sent"    ; folder for sent messages
             mu4e-drafts-folder     "/INBOX.Drafts"  ; unfinished messages
             mu4e-trash-folder      "/INBOX.Trash"   ; trashed messages
             mu4e-refile-folder     "/INBOX.Archive" ; saved messages
             mu4e-get-mail-command  "offlineimap"    ; offlineimap to fetch mail
             mu4e-compose-signature "- Lars"         ; Sign my name
             mu4e-update-interval   (* 5 60)         ; update every 5 min
             mu4e-confirm-quit      nil              ; just quit
             mu4e-view-show-images  t                ; view images
             mu4e-html2text-command
             "html2text -utf8"                       ; use utf-8
             )

       ;; Setup for sending mail.
       (setq user-full-name
             "Lars Tveito"                        ; Your full name
             user-mail-address
             "larstvei@ifi.uio.no"                ; And email-address
             smtpmail-smtp-server
             "smtp.uio.no"                        ; Host to mail-server
             smtpmail-smtp-service 465            ; Port to mail-server
             smtpmail-stream-type 'ssl            ; Protocol used for sending
             send-mail-function 'smtpmail-send-it ; Use smpt to send
             mail-user-agent 'mu4e-user-agent     ; Use mu4e!
             )

       ;; Register file types that can be handled by ImageMagick.
       (when (fboundp 'imagemagick-register-types)
         (imagemagick-register-types))

       ;; A wrapper function to start (if necessary), fetch mail and delete other
       ;; windows.
       (defun show-mu4e ()
         (interactive)
         (mu4e)
         (mu4e-update-mail-and-index t)
         (delete-other-windows))

       ;; Overwrite the native 'compose-mail' binding to 'show-mu4e'.
       (global-set-key (kbd "C-x m") 'show-mu4e))
   #+END_SRC

** Flyspell

   Flyspell offers on-the-fly spell checking. We can enable flyspell for all
   text-modes with this snippet.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (add-hook 'text-mode-hook 'turn-on-flyspell)
   #+END_SRC

   To use flyspell for programming there is =flyspell-prog-mode=, that only
   enables spell checking for comments and strings. We can enable it for all
   programming modes using the =prog-mode-hook=. Flyspell interferes with
   auto-complete mode, but there is a workaround provided by auto complete.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (add-hook 'prog-mode-hook 'flyspell-prog-mode)
     (ac-flyspell-workaround)
   #+END_SRC

** Org

   I use =org-agenda= for appointments and such.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (setq org-agenda-start-on-weekday nil             ; Show agenda from today.
           org-agenda-files '("~/Dropbox/life.org")    ; A list of agenda files.
           org-agenda-default-appointment-duration 120 ; 2 hours appointments.
           )
   #+END_SRC

   When editing org-files with source-blocks, we want the source blocks to
   be themed as they would in their native mode.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (setq org-src-fontify-natively t)
   #+END_SRC

** Interactive functions
   <<sec:defuns>>

   To search recent files useing =ido-mode= we add this snippet from
   [[http://www.emacswiki.org/emacs/CalendarWeekNumbers][EmacsWiki]].

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defun recentf-ido-find-file ()
       "Find a recent file using Ido."
       (interactive)
       (let ((f (ido-completing-read "Choose recent file: " recentf-list nil t)))
         (when f
           (find-file f))))
   #+END_SRC

 =just-one-space= removes all whitespace around a point - giving it a
   negative argument it removes newlines as well. We wrap a interactive
   function around it to be able to bind it to a key.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defun remove-whitespace-inbetween ()
       "Removes whitespace before and after the point."
       (interactive)
       (just-one-space -1))
   #+END_SRC

   This interactive function switches you to a =shell=, and if triggered in
   the shell it switches back to the previous buffer.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defun switch-to-shell ()
       "Jumps to eshell or back."
       (interactive)
       (if (string= (buffer-name) "*shell*")
           (switch-to-prev-buffer)
         (shell)))
   #+END_SRC

   To duplicate either selected text or a line we define this interactive
   function.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defun duplicate-thing ()
       "Ethier duplicates the line or the region"
       (interactive)
       (save-excursion
         (let ((start (if (region-active-p) (region-beginning) (point-at-bol)))
               (end   (if (region-active-p) (region-end) (point-at-eol))))
           (goto-char end)
           (unless (region-active-p)
             (newline))
           (insert (buffer-substring start end)))))
   #+END_SRC

   To tidy up a buffer we define this function borrowed from [[https://github.com/simenheg][simenheg]].

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defun tidy ()
       "Ident, untabify and unwhitespacify current buffer, or region if active."
       (interactive)
       (let ((beg (if (region-active-p) (region-beginning) (point-min)))
             (end (if (region-active-p) (region-end) (point-max))))
         (indent-region beg end)
         (whitespace-cleanup)
         (untabify beg (if (< end (point-max)) end (point-max)))))
   #+END_SRC

** Key bindings

   Bindings for [[https://github.com/magnars/expand-region.el][expand-region]].

   #+BEGIN_SRC emacs-lisp :tangle yes
     (global-set-key (kbd "C-'")  'er/expand-region)
     (global-set-key (kbd "C-;")  'er/contract-region)
   #+END_SRC

   Bindings for [[https://github.com/magnars/multiple-cursors.el][multiple-cursors]].

   #+BEGIN_SRC emacs-lisp :tangle yes
     (global-set-key (kbd "C-c e")  'mc/edit-lines)
     (global-set-key (kbd "C-c a")  'mc/mark-all-like-this)
     (global-set-key (kbd "C-c n")  'mc/mark-next-like-this)
   #+END_SRC

   Bindings for [[http://magit.github.io][Magit]].

   #+BEGIN_SRC emacs-lisp :tangle yes
     (global-set-key (kbd "C-c m") 'magit-status)
   #+END_SRC

   Bindings for [[https://github.com/winterTTr/ace-jump-mode][ace-jump-mode]].

   #+BEGIN_SRC emacs-lisp :tangle yes
     (global-set-key (kbd "C-c SPC") 'ace-jump-mode)
   #+END_SRC

   Bindings for =move-text=.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (global-set-key (kbd "<M-S-up>")    'move-text-up)
     (global-set-key (kbd "<M-S-down>")  'move-text-down)
   #+END_SRC

   Bind some native Emacs functions.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (global-set-key (kbd "C-c s")    'ispell-word)
     (global-set-key (kbd "C-c t")    'org-agenda-list)
     (global-set-key (kbd "C-x k")    'kill-this-buffer)
     (global-set-key (kbd "C-x C-r")  'recentf-ido-find-file)
   #+END_SRC

   Bind the functions defined [[sec:defuns][above]].

   #+BEGIN_SRC emacs-lisp :tangle yes
     (global-set-key (kbd "C-c j")    'remove-whitespace-inbetween)
     (global-set-key (kbd "C-x t")    'switch-to-shell)
     (global-set-key (kbd "C-c d")    'duplicate-thing)
     (global-set-key (kbd "<C-tab>")  'tidy)
   #+END_SRC

** Advice

   An advice can be given to a function to make it behave differently. This
   advice makes =eval-last-sexp= (bound to =C-x C-e=) replace the sexp with
   the value.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defadvice eval-last-sexp (around replace-sexp (arg) activate)
       "Replace sexp when called with a prefix argument."
       (if arg
           (let ((pos (point)))
             ad-do-it
             (goto-char pos)
             (backward-kill-sexp)
             (forward-sexp))
         ad-do-it))
   #+END_SRC

 =Flyspell= signals an error if there is no spell-checking tool is
   installed. We can advice =turn-on=flyspell= and =flyspell-prog-mode= to
   only try to enable =flyspell= if a spell-checking tool is avalible.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defadvice turn-on-flyspell (around check nil activate)
       "Turns on flyspell only if a spell-checking tool is installed."
       (when (executable-find ispell-program-name)
         ad-do-it))
   #+END_SRC

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defadvice flyspell-prog-mode (around check nil activate)
       "Turns on flyspell only if a spell-checking tool is installed."
       (when (executable-find ispell-program-name)
         ad-do-it))
   #+END_SRC

* Language mode specific
** Lisp

 =Pretty-lambda= provides a customizable variable
 =pretty-lambda-auto-modes= that is a list of common lisp modes. Here we
   can add some extra lisp-modes. We run the =pretty-lambda-for-modes=
   function to activate =pretty-lambda-mode= in lisp modes.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (dolist (mode '(slime-repl-mode inferior-lisp-mode inferior-scheme-mode))
       (add-to-list 'pretty-lambda-auto-modes mode))

     (pretty-lambda-for-modes)
   #+END_SRC

   I use =Paredit= when editing lisp code, we enable this for all lisp-modes
   in the =pretty-lambda-auto-modes= list.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (dolist (mode pretty-lambda-auto-modes)
       ;; add paredit-mode to all mode-hooks
       (add-hook (intern (concat (symbol-name mode) "-hook")) 'paredit-mode))
   #+END_SRC

*** Emacs Lisp

    In =emacs-lisp-mode= we can enable =eldoc-mode= to display information
    about a function or a variable in the echo area.

    #+BEGIN_SRC emacs-lisp :tangle yes
      (add-hook 'emacs-lisp-mode-hook 'turn-on-eldoc-mode)
      (add-hook 'lisp-interaction-mode-hook 'turn-on-eldoc-mode)
    #+END_SRC

*** Common lisp

    I use [[http://www.common-lisp.net/project/slime/][Slime]] along with =lisp-mode= to edit Common Lisp code. Slime
    provides code evaluation and other great features, a must have for a
    Common Lisp developer. [[http://www.quicklisp.org/beta/][Quicklisp]] is a library manager for Common Lisp,
    and you can install Slime following the instructions from the site along
    with this snippet.

    #+BEGIN_SRC emacs-lisp :tangle yes
      (when (file-exists-p "~/quicklisp/slime-helper.elc")
        (load (expand-file-name "~/quicklisp/slime-helper.elc")))
    #+END_SRC

    We can specify what Common Lisp program Slime should use (I use SBCL).

    #+BEGIN_SRC emacs-lisp :tangle yes
      (setq inferior-lisp-program "sbcl")
    #+END_SRC

    To improve auto completion for Common Lisp editing we can use =ac-slime=
    which uses slime completions as a source.

    #+BEGIN_SRC emacs-lisp :tangle yes
      (add-hook 'slime-mode-hook 'set-up-slime-ac)
      (add-hook 'slime-repl-mode-hook 'set-up-slime-ac)

      (eval-after-load "auto-complete"
        '(add-to-list 'ac-modes 'slime-repl-mode))
    #+END_SRC

*** Scheme

    [[http://www.nongnu.org/geiser/][Geiser]] provides features similar to Slime for Scheme editing. Everything
    works pretty much out of the box, the only thing we need to add is the
    auto completion.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (add-hook 'geiser-mode-hook 'ac-geiser-setup)
     (add-hook 'geiser-repl-mode-hook 'ac-geiser-setup)
     (eval-after-load "auto-complete"
       '(add-to-list 'ac-modes 'geiser-repl-mode))
   #+END_SRC

** Java and C

   The =c-mode-common-hook= is a general hook that work on all C-like
   languages (C, C++, Java, etc...). I like being able to quickly compile
   using =C-c C-c= (instead of =M-x compile=), a habit from =latex-mode=.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defun c-setup ()
       (local-set-key (kbd "C-c C-c") 'compile))

     (add-hook 'c-mode-common-hook 'c-setup)
   #+END_SRC

   Some statements in Java appear often, and become tedious to write
   out. We can use abbrevs to speed this up.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (define-abbrev-table 'java-mode-abbrev-table
       '(("psv" "public static void main(String[] args) {" nil 0)
         ("sopl" "System.out.println" nil 0)
         ("sop" "System.out.printf" nil 0)))
   #+END_SRC

   To be able to use the abbrev table defined above, =abbrev-mode= must be
   activated.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defun java-setup ()
       (abbrev-mode t)
       (setq-local compile-command (concat "javac " (buffer-name))))

     (add-hook 'java-mode-hook 'java-setup)
   #+END_SRC

** Assembler

   When writing assembler code I use =#= for comments. By defining
 =comment-start= we can add comments using =M-;= like in other programming
   modes. Also in assembler should one be able to compile using =C-c C-c=.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (defun asm-setup ()
       (setq comment-start "#")
       (local-set-key (kbd "C-c C-c") 'compile))

     (add-hook 'asm-mode-hook 'asm-setup)
   #+END_SRC

** LaTeX

 =.tex=-files should be associated with =latex-mode= instead of
 =tex-mode=.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (add-to-list 'auto-mode-alist '("\\.tex\\'" . latex-mode))
   #+END_SRC

   I like using the [[https://code.google.com/p/minted/][Minted]] package for source blocks in LaTeX. To make org
   use this we add the following snippet.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (add-to-list 'org-latex-packages-alist '("" "minted"))
     (setq org-latex-listings 'minted)
   #+END_SRC

   Because [[https://code.google.com/p/minted/][Minted]] uses [[http://pygments.org][Pygments]] (an external process), we must add the
 =-shell-escape= option to the =org-latex-pdf-process= commands.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (setq org-latex-pdf-process
           (mapcar
            (lambda (str)
              (concat "pdflatex -shell-escape "
                      (substring str (string-match "-" str))))
            org-latex-pdf-process))
   #+END_SRC

** Python

   [[http://tkf.github.io/emacs-jedi/released/][Jedi]] offers very nice auto completion for =python-mode=. Mind that it is
   dependent on some python programs as well, so make sure you follow the
   instructions from the site.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (setq jedi:server-command
           (cons "python3" (cdr jedi:server-command))
           python-shell-interpreter "python3")
     (add-hook 'python-mode-hook 'jedi:setup)
     (setq jedi:complete-on-dot t)
     (add-hook 'python-mode-hook 'jedi:ac-setup)
   #+END_SRC

** Haskell

 =haskell-doc-mode= is similar to =eldoc=, it displays documentation in
   the echo area. Haskell has several indentation modes - I prefer using
 =haskell-indent=.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (add-hook 'haskell-mode-hook 'turn-on-haskell-doc-mode)
     (add-hook 'haskell-mode-hook 'turn-on-haskell-indent)
   #+END_SRC

** Matlab

   Matlab is very similar to Octave, which is supported by Emacs. We just
   need to let =.m=-files be associated with =octave-mode=.

   #+BEGIN_SRC emacs-lisp :tangle yes
     (add-to-list 'auto-mode-alist '("\\.m$" . octave-mode))
   #+END_SRC