signal datum &rest arguments → nil

datum, arguments — designators for a condition of default type simple-condition.

Signals the condition denoted by the given datum and arguments. If the condition is not handled, signal returns nil.

 (defun handle-division-conditions (condition) 
   (format t "Considering condition for division condition handling~%") 
   (when (and (typep condition 'arithmetic-error) 
              (eq '/ (arithmetic-error-operation condition))) 
     (invoke-debugger condition))) 
HANDLE-DIVISION-CONDITIONS 
 (defun handle-other-arithmetic-errors (condition) 
   (format t "Considering condition for arithmetic condition handling~%") 
   (when (typep condition 'arithmetic-error) 
     (abort))) 
HANDLE-OTHER-ARITHMETIC-ERRORS 
 (define-condition a-condition-with-no-handler (condition) ()) 
A-CONDITION-WITH-NO-HANDLER 
 (signal 'a-condition-with-no-handler) 
NIL 
 (handler-bind ((condition #'handle-division-conditions) 
                  (condition #'handle-other-arithmetic-errors)) 
   (signal 'a-condition-with-no-handler)) 
Considering condition for division condition handling 
Considering condition for arithmetic condition handling 
NIL 
 (handler-bind ((arithmetic-error #'handle-division-conditions) 
                  (arithmetic-error #'handle-other-arithmetic-errors)) 
   (signal 'arithmetic-error :operation '* :operands '(1.2 b))) 
Considering condition for division condition handling 
Considering condition for arithmetic condition handling 
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The debugger might be entered due to *break-on-signals*.

Handlers for the condition being signaled might transfer control.

Existing handler bindings.

*break-on-signals*

*break-on-signals*, error, simple-condition, Section 9.1.4 (Signaling and Handling Conditions)

If (typep datum *break-on-signals*) yields true, the debugger is entered prior to beginning the signaling process. The continue restart can be used to continue with the signaling process. This is also true for all other functions and macros that should, might, or must signal conditions.