filtered-functions
Filtered functions provide an extension of generic function invocation that add a simple preprocessing step before the actual method dispatch is performed and thus enable the use of arbitrary predicates for selecting and applying methods.
$ area51 add filtered-functionsCopyUsage
;; area51 add updates your .asd automatically.
;; Use the package in your code:
(in-package :my-project)
(filtered-functions:some-function ...)