3.2 Install a Function Definition

If you are reading this inside of Info in Emacs, you can try out the multiply-by-seven function by first evaluating the function definition and then evaluating (multiply-by-seven 3). A copy of the function definition follows. Place the cursor after the last parenthesis of the function definition and type C-x C-e. When you do this, multiply-by-seven will appear in the echo area. (What this means is that when a function definition is evaluated, the value it returns is the name of the defined function.) At the same time, this action installs the function definition.

(defun multiply-by-seven (number)
  "Multiply NUMBER by seven."
  (* 7 number))

By evaluating this defun, you have just installed multiply-by-seven in Emacs. The function is now just as much a part of Emacs as forward-word or any other editing function you use. (multiply-by-seven will stay installed until you quit Emacs. To reload code automatically whenever you start Emacs, see Installing Code Permanently.)