Rodrigo Canellas <rodrigo.canellas@tqtvd.com> writes:
  

I would like to insert a single space after certain characters, such
as '+', '-', '&', '=', etc.

I think I can do this with a hook lisp function, but I do not know how.
    

I assume you don't what this to occur everywhere, only in a certain mode.

That means that you will have to locate that mode hook variable (M-x
apropos RET <the-mode> hook RET), and add to it some "meat", that is a
function that will customize the behavior of these keys,  by modifying
the local bindings of the buffer.

(defun self-insert-and-space-command ()
  (interactive)
  (insert last-command-char " "))

M-x local-set-key RET + RET self-insert-and-space-command RET


If it's ok, then define your meat:

(defun <the-mode>-meat ()
   (dolist (key (list (kbd "+")
                      (kbd "-")
                      (kbd "&")
                      (kbd "=")))
      (local-set-key key 'self-insert-and-space-command)))


Then hook the meat:

(add-hook '<the-mode>-hook  '<the-mode>-meat)


When you test the hook, be sure to kill and reopen the buffer, or
directly execute the meat with M-: (<the-mode>-meat) RET