(This is a repost of an old blog post of mine from Teknik.)
TIL that I can do:
(define-condition my-condition () ()) (defmethod initialize-instance :after ((warning my-condition) &key) (print "boo"))
The works on SBCL*, CCL, ECL, ABCL, CLISP.
*You need to use
MAKE-INSTANCE instead of
MAKE-CONDITION to make the constructor fire on SBCL. See https://bugs.launchpad.net/sbcl/+bug/1761735