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5.1.1 Debugger Banner

When you enter the debugger, it looks something like this:

     debugger invoked on a TYPE-ERROR in thread 11184:
       The value 3 is not of type LIST.
     
     You can type HELP for debugger help, or (SB-EXT:QUIT) to exit from SBCL.
     
     restarts (invokable by number or by possibly-abbreviated name):
       0: [ABORT   ] Reduce debugger level (leaving debugger, returning to toplevel).
       1: [TOPLEVEL] Restart at toplevel READ/EVAL/PRINT loop.
     (CAR 1 3)
     0]

The first group of lines describe what the error was that put us in the debugger. In this case car was called on 3, causing a type-error.

This is followed by the “beginner help line”, which appears only if sb-ext:*debugger-beginner-help* is true (default).

Next comes a listing of the active restart names, along with their descriptions – the ways we can restart execution after this error. In this case, both options return to top-level. Restarts can be selected by entering the corresponding number or name.

The current frame appears right underneath the restarts, immediately followed by the debugger prompt.