invoke-debugger condition →|

condition — a condition object.

invoke-debugger attempts to enter the debugger with condition.

If *debugger-hook* is not nil, it should be a function (or the name of a function) to be called prior to entry to the standard debugger. The function is called with *debugger-hook* bound to nil, and the function must accept two arguments: the condition and the value of *debugger-hook* prior to binding it to nil. If the function returns normally, the standard debugger is entered.

The standard debugger never directly returns. Return can occur only by a non-local transfer of control, such as the use of a restart function.

 (ignore-errors ;Normally, this would suppress debugger entry 
   (handler-bind ((error #'invoke-debugger)) ;But this forces debugger entry 
     (error "Foo."))) 
Debug: Foo. 
To continue, type :CONTINUE followed by an option number: 
 1: Return to Lisp Toplevel. 
Debug>

*debugger-hook* is bound to nil, program execution is discontinued, and the debugger is entered.

*debug-io* and *debugger-hook*.

error, break