(defun one-of (choices &optional (prompt "Choice"))
  (let ((n (length choices)) (i))
    (do ((c choices (cdr c)) (i 1 (+ i 1)))
        ((null c))
      (format t "~&[~D] ~A~%" i (car c)))
    (do () ((typep i `(integer 1 ,n)))
      (format t "~&~A: " prompt)
      (setq i (read))
      (fresh-line))
    (nth (- i 1) choices)))

(defun my-debugger (condition me-or-my-encapsulation)
  (format t "~&Fooey: ~A" condition)
  (let ((restart (one-of (compute-restarts))))
    (if (not restart) (error "My debugger got an error."))
    (let ((*debugger-hook* me-or-my-encapsulation))
      (invoke-restart-interactively restart))))

(let ((*debugger-hook* #'my-debugger))
  (+ 3 'a))
>>  Fooey: The argument to +, A, is not a number.
>>   [1] Supply a replacement for A.
>>   [2] Return to Cloe Toplevel.
>>  Choice: 1
>>   Form to evaluate and use: (+ 5 'b)
>>   Fooey: The argument to +, B, is not a number.
>>   [1] Supply a replacement for B.
>>   [2] Supply a replacement for A.
>>   [3] Return to Cloe Toplevel.
>>  Choice: 1
>>   Form to evaluate and use: 1
=>  9