Merge pull request #588 from felixwellen/auto-delete-whitespaces

Emacs-lisp code for deleting whitespaces on save

CONTRIBUTING.md

@@ -64,7 +64,16 @@ When preparing a PR here are some general guidelines:
   editing files by adding `(setq-default show-trailing-whitespace t)`
   to `~/.emacs`. The command `M-x delete-trailing-whitespace` is also
   very useful. It is possible to add a hook that runs this command
-  automatically when saving Agda files.
+  automatically when saving Agda files, by adding the following to your
+  `~/.emacs`:
+  ```
+  ;; delete trailing whitespace before saving in agda-mode
+  (defun agda-mode-delete-whitespace-before-save ()
+    (when (eq major-mode 'agda2-mode)
+      (delete-trailing-whitespace)))
+
+  (add-hook 'before-save-hook #'agda-mode-delete-whitespace-before-save)
+  ```
 
 - Use copattern-matching when instantiating records for efficiency.
   This seems especially important when constructing Iso's.