(require 'closer-mop) ;; 1

(defmacro gen () ;; 2
  (let ((type (sb-mop:slot-definition-type
               (first (sb-mop:class-slots (find-class 'A))))))
    (unless (equal type 'boolean) (error "No type specified for the slot."))))

(progn ;; 3
  (defclass A () ((x :type boolean))) ;; (x :type boolean) -> (x)
  (c2mop:ensure-finalized (find-class 'A))
  (gen))

#| SBCL 2.0.5, using sly
1. eval-defun expressions 1 and 2
2. compile-defun expression 3
3. observe error: "no class named common-lisp-user::a"
4. compile-defun again, error is gone
5. remove type specification in class A
6. compile-defun expression 3, observe no error
7. compile-defun expression 3 again, observe error ("No type specified for the slot")
No such behavior is observed when using eval-defun.
What's happening here?
|#