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  ANSI Common Lisp   9 Conditions   9.1 Condition System Concepts   9.1.4 Signaling and Handling Conditions

9.1.4.1 Signaling

When a condition is signaled, the most recent applicable active handler is invoked. Sometimes a handler will decline by simply returning without a transfer of control. In such cases, the next most recent applicable active handler is invoked.

If there are no applicable handlers for a condition that has been signaled, or if all applicable handlers decline, the condition is unhandled.

The functions cerror and error invoke the interactive condition handler (the debugger) rather than return if the condition being signaled, regardless of its type, is unhandled. In contrast, signal returns nil if the condition being signaled, regardless of its type, is unhandled.

The variable *break-on-signals* can be used to cause the debugger to be entered before the signaling process begins.

The next figure shows defined names relating to the signaling of conditions.

Defined names relating to signaling conditions.
*break-on-signals* error warn
cerror signal

9.1.4.1.1  Resignaling a Condition


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