signal

ToC

Allegro CL

ANSI Common Lisp

9 Conditions

9.2 Dictionary of Conditions

9.2.17 signal

Function

Syntax:

signal datum &rest arguments

nil

Arguments and Values:

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

Description:

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

Examples:

 (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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Side Effects:

The debugger might be entered due to *break-on-signals*.

Handlers for the condition being signaled might transfer control.

Affected By:

Existing handler bindings.

*break-on-signals*

Notes:

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.

Allegro CL Implementation Details:

None.