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4.2 Debugger Command Loop

The debugger is an interactive read-eval-print loop much like the normal top level, but some symbols are interpreted as debugger commands instead of being evaluated. A debugger command starts with the symbol name of the command, possibly followed by some arguments on the same line. Some commands prompt for additional input. Debugger commands can be abbreviated by any unambiguous prefix: help can be typed as `h', `he', etc.

The package is not significant in debugger commands; any symbol with the name of a debugger command will work. If you want to show the value of a variable that happens also to be the name of a debugger command you can wrap the variable in a progn to hide it from the command loop.

The debugger prompt is “frame]”, where frame is the number of the current frame. Frames are numbered starting from zero at the top (most recent call), increasing down to the bottom. The current frame is the frame that commands refer to.

It is possible to override the normal printing behaviour in the debugger by using the sb-ext:*debug-print-variable-alist*.

— Variable: sb-ext:*debug-print-variable-alist*

an association list describing new bindings for special variables to be used within the debugger. Eg. 

           ((*PRINT-LENGTH* . 10) (*PRINT-LEVEL* . 6) (*PRINT-PRETTY* . NIL))

The variables in the car positions are bound to the values in the cdr during the execution of some debug commands. When evaluating arbitrary expressions in the debugger, the normal values of the printer control variables are in effect.

Initially empty, *debug-print-variable-alist* is typically used to provide bindings for printer control variables.