If you look at the literature there are numerous examples of extensible macros. Often this is done for rule-based systems, which also involves matching or unifi

If you look at the literature there are numerous examples of extensible macros. Often this is done for rule-based systems, which also involves matching or unification. Typically one wants to define these rules individually, update them individually, etc. One needs a registry, an interning function and a driving function. Below is just an example: (defvar *patterns* (make-hash-table)) (defparameter *pattern-names* nil) (defun intern-pattern (name if-pattern then-pattern) (setf *pattern-names* (append *pattern-names* (list name))) (setf (gethash name *patterns*) (list (compile nil `(lambda (pat) ,if-pattern)) (compile nil `(lambda (pat expr then else) (declare (ignorable pat expr then else)) ,then-pattern)))) name) (defmacro if-match (pat expr then else) (loop for name in *pattern-names* for (if-part then-part) = (gethash name *patterns*) when (funcall if-part pat) do (return (funcall then-part pat expr then else)))) (intern-pattern 'variable '(and pat (symbolp pat)) '`(let ((,pat ,expr)) ,then)) (intern-pattern 'literal-atom '(atom pat) '`(if (equalp ',pat ,expr) ,then ,else)) (intern-pattern 'cons '(eq 'cons (car pat)) '(destructuring-bind (_ p-car p-cdr) pat (declare (ignore _)) (let ((tmp (gensym))) `(let ((,tmp ,expr)) (if (consp ,tmp) (if-match ,p-car (car ,tmp) (if-match ,p-cdr (cdr ,tmp) ,then ,else) ,else) ,else))))) Writing the macro DEFPATTERN is then trivial... I help maintain an old Lisp-based web server, which was written in the mid-90s on the Symbolics Lisp Machine. It literally has zillions of these registry/intern/machinery/defining-macro combinations... It's just: one has to program those. But it has been done many many many times.