To set a breakpoint, for example at the call to
in one of your functions:
Alt+Ctrl+Qin Emacs emulation).
Toggle Breakpoint. The symbol
+is highlighted red indicating that a breakpoint is set.
When the breakpoint is reached, a Stepper tool is invoked, allowing you to step through the code, add further breakpoints, and so on. See The Stepper for more information about the Stepper tool.
LispWorks IDE User Guide (Windows version) - 25 Nov 2011