: ) wonderful world ( :

ContextL is a part of the Closer project with contributions from Pascal Costanza and probably others. As per the code repository, it’s actively developed.

(defpackage :a-test
  (:use :cl))

(in-package :a-test)

(contextl:define-layered-class
    bar ()
    ((value :initarg :value :layered-accessor bar-value)))

(contextl:define-layered-function bar-incf (f))

(contextl:define-layered-method
    bar-incf ((b bar))
    (incf (bar-value b)))

(contextl:deflayer log-layer)

(contextl:define-layered-class
    bar :in log-layer ()
    ())

(contextl:define-layered-method
    bar-incf :in log-layer :around ((b bar))
    (progn
      (princ (format nil "~A is incfed" b))
      (call-next-method)))

(defparameter +a-bar+
  (make-instance 'bar :value 11))

And now, the REPL:

A-TEST> +a-bar+
#<BAR {BEB2581}>
A-TEST> (bar-value +a-bar+)
11
A-TEST> (bar-incf +a-bar+)
12
A-TEST> (bar-value +a-bar+)
12
A-TEST> (contextl:with-active-layers (log-layer) (bar-incf +a-bar+))
#<BAR {BEB2581}> is incfed
13
A-TEST> (bar-value +a-bar+)
13
A-TEST>