Emacs, how to write a shortcut calling a function with as argument the word at the cursor position?

Question

How do I set up a shortcut for Emacs that will call a function and take as an argument the word at the cursor position? Like alt . in rtags package.

Answer 1

Version that reads only names of functions, with completion:

(defun call-fun-on-word-at-point (function word)
  "Call FUNCTION with argument WORD, the word at point."
  (interactive 
   (list (intern (completing-read "Function: " obarray 'functionp t))
         (word-at-point)))
  (funcall function word))

Version that reads a Lisp expression as a function (name or lambda expression):

(defun call-fun-on-word-at-point (function word)
  "Call FUNCTION with argument WORD, the word at point."
  (interactive 
   (let (fun)
     (while (not (functionp fun))
       (setq fun  (read--expression "Function: "))
       (when (stringp fun) (setq fun  (intern fun))))
     (list fun (word-at-point))))
  (funcall function word))

As for a "shortcut", I guess you're asking to bind the command to a key.

(global-set-key (kbd "M-.") 'call-fun-on-word-at-point)