Auto-setup of Haskell with syntax checking and completion. Requires following cabal packages: happy, alex, ghc-mod. Put this file in ~/.emacs.d/init.el

init.el

(require 'package)
(setq package-list '(markdown-mode
                     yaml-mode
                     js2-mode
                     find-file-in-project
                     auto-complete
                     ghc
                     haskell-mode
                     flycheck
                     flycheck-haskell
                     ))
(add-to-list 'package-archives
             '("melpa" . "http://melpa.org/packages/") t)

;; activate all the packages (in particular autoloads)
(package-initialize)

;; fetch the list of packages available
(unless package-archive-contents
  (package-refresh-contents))

;; install the missing packages
(dolist (package package-list)
  (unless (package-installed-p package)
        (package-install package)))

(when (not package-archive-contents)
    (package-refresh-contents))
;; NO FRILLS
(dolist (mode '(menu-bar-mode tool-bar-mode scroll-bar-mode))
  (when (fboundp mode) (funcall mode -1)))
(setq inhibit-startup-screen t)
;; NO JUNK
(setq auto-save-file-name-transforms `((".*" ,temporary-file-directory t))
      backup-directory-alist `((".*" . ,temporary-file-directory)))
;; HASKELL
(require 'auto-complete)
(require 'auto-complete-config)
(ac-config-default)

(add-hook 'flycheck-mode-hook 'flycheck-haskell-setup)
(autoload 'ghc-init "ghc" nil t)

(defun el-get-ghc-mod-hook ()
  (ghc-init)
  (flycheck-mode))
(add-hook 'haskell-mode-hook 'el-get-ghc-mod-hook)

(add-hook 'haskell-mode-hook 'turn-on-haskell-doc-mode)
(add-hook 'haskell-mode-hook 'turn-on-haskell-indentation)
(setq haskell-process-type 'cabal-repl
      haskell-process-args-cabal-repl '("--ghc-option=-ferror-spans"))
(define-key haskell-mode-map (kbd "C-x C-d") nil)
(define-key haskell-mode-map (kbd "C-c C-z") 'haskell-interactive-switch)
(define-key haskell-mode-map (kbd "C-c C-l") 'haskell-process-load-file)
(define-key haskell-mode-map (kbd "C-c C-b") 'haskell-interactive-switch)
(define-key haskell-mode-map (kbd "C-c C-t") 'haskell-process-do-type)
(define-key haskell-mode-map (kbd "C-c C-i") 'haskell-process-do-info)
(define-key haskell-mode-map (kbd "C-c M-.") nil)
(define-key haskell-mode-map (kbd "C-c C-d") nil)
(define-key haskell-mode-map (kbd "C-c v c") 'haskell-cabal-visit-file)
;; auto-complete

(ac-define-source haskell
  '((candidates
     . (lambda ()
         (let ((resp (haskell-process-get-repl-completions (haskell-process) ac-prefix)))
           (if (string= (car resp) "")
               (cdr resp)
             (mapcar (lambda (s) (car resp)) (cdr resp))))))))

(add-hook 'haskell-mode-hook '(lambda ()
        (add-to-list 'ac-sources 'ac-source-haskell)))
;; END HASKELL


(column-number-mode)
(setq-default indent-tabs-mode nil)
(define-key global-map (kbd "RET") 'newline-and-indent)
;;(load-theme 'solarized-dark t)

(require 'js2-mode)
(add-to-list 'auto-mode-alist '("\\.js$" . js2-mode))

;;(add-to-list 'auto-mode-alist '("\\.purs$" . haskell-mode))

;;(custom-set-variables
;; '(js2-basic-offset 2)
;; '(js2-bounce-indent-p t)
;;)

(global-set-key (kbd "C-x f") 'find-file-in-project)

(defun set-exec-path-from-shell-PATH ()
(let ((path-from-shell (replace-regexp-in-string
"[ \t\n]*$"
""
(shell-command-to-string "$SHELL --login -i -c 'echo $PATH'"))))
(setenv "PATH" path-from-shell)
(setq eshell-path-env path-from-shell) ; for eshell users
(setq exec-path (split-string path-from-shell path-separator))))

(when window-system (set-exec-path-from-shell-PATH))

(global-set-key (kbd "M-3") '(lambda () (interactive) (insert "#")))