HOWTO

CALLING AN EMACS LISP FUNCTION FROM COMMON LISP
===============================================

All Emacs Lisp symbols are accessible from the EMACS-LISP package
nicknamed EL.  Remember that by default, Common Lisp converts symbol
names to upper case, so use | to prevent that.  For example, to print
a message in the echo area:

  (el:|message| "Hello Emacs!")


WRITING AN INTERACTIVE EMACS COMMAND
====================================

Enter these functions at the interactive prompt:

  (defun fac (n) (if (< n 2) 1 (* n (fac (1- n)))))

  (defun el:|my-fun| (n)
    "Print n!"
    (declare (interactive "nEnter a number: "))
    (el:|message| (format nil "~D! is ~D" n (fac n))))

Now, try it with "M-x my-fun".


CALLING A COMMON LISP FUNCTION FROM EMACS LISP
==============================================

If it's a standard Common Lisp function, it's probably available in
Emacs Lisp with an all-uppercase name.  For example

  (READ-FROM-STRING "#.(+ 1 2)")
  => 3

Otherwise, you'll find the symbol in the package in which you defined
the function.  For example, if you defined the function above at the
"COMMON-LISP-USER>" prompt:

  (FIND-SYMBOL "FAC" "CL-USER")

For easy access from Emacs Lisp, you may store the function in a local
symbol:

  (fset 'fac (symbol-function (FIND-SYMBOL "FAC" "CL-USER")))

Now you can call (fac 10).