emacs lisp: define function to be used inside emacs

stateless · 03-01-2013, 03:24 PM

Hi. I'm going to be reading through the whole Emacs lisp manual, but I already know a bit of common lisp, and was hoping to get enough "working knowledge" quickly to play around with making functions I can call and use within Emacs. For example, how would I define a function which would allow me to enter

Code:

M-x negate <RET> -2 <RET>

and see "2" displayed in the minibuffer.

ntubski · 03-01-2013, 05:04 PM

You could start with a non-interactive version of the function, which will look the same as the Common Lisp version:

Code:

(defun negate (n)
  (- n)) ; put the point (cursor) on the definition and hit C-M-x
         ; (Ctrl+Alt+X) to define the function

(negate -2) ; C-M-x here to test it

Then make it interactive by using the interactive form, and using the message function instead of returning the value:

Code:

(defun negate (n)
  (interactive "NEnter a number: ")
  (message "%d" (- n)))