My simplest Emacs configuration

init.el

(menu-bar-mode -1)
(global-hl-line-mode 1)
(setq hl-line-face 'underline)
(setq mode-require-final-newline nil)
(setq-default tab-width 4)
(setq-default indent-tabs-mode nil)
(show-paren-mode t)
(global-linum-mode t)
(setq linum-format "%d ")

(setq make-backup-files nil)
(setq auto-save-default nil)

(require 'package)
(add-to-list 'package-archives '("melpa" . "http://melpa.milkbox.net/packages/") t)
(add-to-list 'package-archives '("marmalade" . "http://marmalade-repo.org/packages/"))
(package-initialize)

(unless (package-installed-p 'undo-tree)
  (package-refresh-contents) (package-install 'undo-tree))

(unless (package-installed-p 'scala-mode)
  (package-refresh-contents) (package-install 'scala-mode))

(unless (package-installed-p 'yaml-mode)
  (package-refresh-contents) (package-install 'yaml-mode))

(unless (package-installed-p 'atom-dark-theme)
  (package-refresh-contents) (package-install 'atom-dark-theme))

(unless (package-installed-p 'helm)
  (package-refresh-contents) (package-install 'helm))

(unless (package-installed-p 'helm-ls-git)
  (package-refresh-contents) (package-install 'helm-ls-git))

(unless (package-installed-p 'helm-ag)
  (package-refresh-contents) (package-install 'helm-ag))

(load-theme 'atom-dark t)

(add-hook 'scala-mode-hook 'my-scala-mode-hook)
(defun my-scala-mode-hook ()
  (setq scala-indent:use-javadoc-style t))

(require 'helm)
(helm-mode 1)
(define-key global-map (kbd "C-x C-f") 'helm-find-files)
(define-key global-map (kbd "C-x C-b") 'helm-buffers-list)
(define-key global-map (kbd "C-x C-o") 'helm-mini)
(define-key global-map (kbd "C-x C-d") 'helm-browse-project)
(define-key global-map (kbd "M-x") 'helm-M-x)
(define-key global-map (kbd "C-x C-g") 'helm-ag)
(define-key global-map (kbd "C-x C-r") 'helm-resume)
(define-key global-map (kbd "M-y") 'helm-show-kill-ring)

(require 'undo-tree)
(global-undo-tree-mode)