The backtrace area displays the function calls on the execution stack. Each tree root or list item in the backtrace area represents a stack frame associated with a function call.
Double-clicking on any stack frame finds and displays the source code definition for that function in the Editor, if this is known. Any frame selected in this area can be operated on using the commands in the Frame menu, which is also available as the context menu. See Performing operations on stack frames for details.
The backtrace is displayed either in a tree or a list, with the behaviors described below.
You can choose which type of display it uses by the Frames and Arguments preference, described in Configuring the debugger tool.
LispWorks IDE User Guide (Macintosh version) - 25 Nov 2011