(define-condition mycond ()
  ((myvar :accessor myvar :initarg myvar)))

(handler-case
    (signal 'mycond :myvar 1) 
  (mycond (c) (myvar c))) ; Error

(handler-bind ((mycond
                 #'(lambda (c)
                     (print (myvar c))))) ; Error
  (signal 'mycond :myvar 1))

(myvar (make-condition 'mycond :myvar 10))

; Evaluation aborted on #<SIMPLE-ERROR "Unbound condition slot: ~S" {1004348AD3}>.