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Starter Kit Scala

This is part of the Emacs Starter Kit.

Starter Kit Scala

Support for developing in Scala under Emacs.

Scala-mode2

This is a new scala major mode for emacs 24. It is a complete rewrite based on the Scala Language Specification 2.9.

The mode intends to provide the basic emacs support, including:

  • indenting of code, comments and multi-line strings
  • motion commands
  • highlighting

Currently the indenting of code has been finalized. Highlighting is under work. No scala specific motion commands have been added, but standard emacs motions work of course.

Install scala-mode2

Install scala-mode2 from MELPA (M-x package-install RET scala-mode2)

(starter-kit-install-if-needed 'scala-mode2)

Customise scala-mode2

(add-hook 'scala-mode-hook '(lambda ()

  ;; Bind the 'newline-and-indent' command to RET (aka 'enter'). This
  ;; is normally also available as C-j. The 'newline-and-indent'
  ;; command has the following functionality: 1) it removes trailing
  ;; whitespace from the current line, 2) it create a new line, and 3)
  ;; indents it.  An alternative is the
  ;; 'reindent-then-newline-and-indent' command.
  (local-set-key (kbd "RET") 'newline-and-indent)

  ;; Alternatively, bind the 'newline-and-indent' command and
  ;; 'scala-indent:insert-asterisk-on-multiline-comment' to RET in
  ;; order to get indentation and asterisk-insertion within multi-line
  ;; comments.
  (local-set-key (kbd "RET")
                 '(lambda ()
                    (interactive)
                    (newline-and-indent)
                    (scala-indent:insert-asterisk-on-multiline-comment)))

  ;; Bind the backtab (shift tab) to
  ;; 'scala-indent:indent-with-reluctant-strategy command. This is usefull
  ;; when using the 'eager' mode by default and you want to "outdent" a
  ;; code line as a new statement.
  (local-set-key (kbd "<backtab>") 'scala-indent:indent-with-reluctant-strategy)))

sbt-mode

An emacs mode for interacting with sbt, scala console (aka REPL) and sbt projects.

The mode provides basic functionality required for successfully interacting with sbt from emacs. The core functionality includes:

  • interacting with sbt shell and scala console
  • compiling code and navigating to errors
  • finding things in code

Install sbt-mode

Install sbt-mode2 from MELPA (M-x package-install RET sbt-mode)

(starter-kit-install-if-needed 'sbt-mode)

Customise sbt-mode

To work efficiently with sbt-mode, you should customize these variables.

  • sbt:program-name - the name of the sbt executable, defaults to

sbt. Note: this variable is best configured throught the emacs customization menu (M-x customize-variable RET sbt:program-name) or set globally. You can not set it with the mode hook.

  • grep-find-ignored-directories - directories not to include in

searches. You should add the target directory and maybe remove many of the directories related to arcane version control tools that you will not have anyway.

  • grep-find-ignored-files - a list of file patterns to ignore in searches.

You may also want to add a mode-hook to you .emacs file that alters key-bindings and some settings.

(add-hook 'sbt-mode-hook '(lambda ()
  ;; compilation-skip-threshold tells the compilation minor-mode
  ;; which type of compiler output can be skipped. 1 = skip info
  ;; 2 = skip info and warnings.
  (setq compilation-skip-threshold 1)

  ;; Bind C-a to 'comint-bol when in sbt-mode. This will move the
  ;; cursor to just after prompt.
  (local-set-key (kbd "C-a") 'comint-bol)

  ;; Bind M-RET to 'comint-accumulate. This will allow you to add
  ;; more than one line to scala console prompt before sending it
  ;; for interpretation. It will keep your command history cleaner.
  (local-set-key (kbd "M-RET") 'comint-accumulate)))

Besides customizing sbt-mode, you might also want to add some customizations to your scala-mode2 key-bindings. The following two commands are good to have in some easily accessible key position.

(add-hook 'scala-mode-hook '(lambda ()
   ;; sbt-find-definitions is a command that tries to find (with grep)
   ;; the definition of the thing at point.
   (local-set-key (kbd "M-.") 'sbt-find-definitions)
   
   ;; use emacs M-x next-error to navigate errors
   (local-set-key (kbd "M-'") 'next-error)
   ;; use sbt-run-previous-command to re-compile your code after changes
   (local-set-key (kbd "C-x '") 'sbt-run-previous-command)))

Ensime

ENSIME is the ENhanced Scala Interaction Mode for Emacs. It provides many features that are commonly found only in IDEs, such as live error-checking, symbol inspection, package/type browsing, and basic refactoring.

Install Ensime

(starter-kit-install-if-needed 'ensime)

Yasnippet

Provide templates for many standard operations.

Install Yasnippet

(starter-kit-install-if-needed 'yasnippet)

Configure Yasnippet

(add-hook 'scala-mode-hook '(lambda ()
  (yas-minor-mode)))

Whitespace

Emacs has a very nice minor mode for highlighting bad whitespace and removing any unwanted whitespace when you save a file. To use it, uncomment the expression below

Configure Whitespace

(add-hook 'scala-mode-hook '(lambda ()
  ;;(require 'whitespace)
  ;; clean-up whitespace at save
  (make-local-variable 'before-save-hook)
  (add-hook 'before-save-hook 'whitespace-cleanup)

  ;; turn on highlight. To configure what is highlighted, customize
  ;; the *whitespace-style* variable. A sane set of things to
  ;; highlight is: face, tabs, trailing
  (whitespace-mode)))