debugger-hook (original) (raw)

ANSI Common Lisp 9 Conditions 9.2 Dictionary of Conditions

Value Type:

a designator for a function of two arguments (a condition and the value of *debugger-hook* at the time the debugger was entered), or nil.

Initial Value:

nil.

Description:

When the value of *debugger-hook* is non-nil, it is called prior to normal entry into the debugger, either due to a call to invoke-debuggeror due to automatic entry into the debugger from a call to erroror cerror with a condition that is not handled. The function may either handle the condition(transfer control) or return normally (allowing the standard debugger to run). To minimize recursive errors while debugging,*debugger-hook* is bound to nil by invoke-debuggerprior to calling the function.

Examples:

(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

Affected By:

invoke-debugger

Notes:

When evaluating code typed in by the user interactively, it is sometimes useful to have the hook function bind *debugger-hook* to the_function_ that was its second argument so that recursive errors can be handled using the same interactive facility.

Allegro CL Implementation Details:

None.