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ACL Debugger Commands

ACL Debugger Commands

When Allegro Common Lisp (the Lisp dialect used for the Pathway Tools) detects some sort of error, it enters Debugger mode.

Here is a sample of what is printed before the debugger is entered. The fact that the last line begins with a number within small brackets indicates that the debugger is active.

Error: Received signal number 2 (Keyboard interrupt)
  [condition type: INTERRUPT-SIGNAL]

Restart actions (select using :continue):
 0: continue computation
[1c] EC(13): 
A number of special commands are available from within the debugger. Debugger commands begin with a colon character. We list abbreviations for these commands within parentheses.

Basic Debugger Commands

  • :reset (:res) -- Exits from the debugger back to the Lisp top level
  • :pop (:po) -- Finishes the current debugger level -- if you have entered the debugger when the debugger was already active, this commands pops back to the previously entered level of the debugger.
  • :continue (:cont) -- Resumes execution, assuming the error is continuable. You can include a number, e.g., ":cont 3", to invoke the "restart action" listed just above the debugger prompt line.

Advanced Debugger Commands

  • :zoom (:zo) -- Print the execution stack
  • :up/:down -- Move up or down the stack to a new frame
  • :local (:loc) -- Print all local variables in the current stack frame (with no arguments), or print a specified local variable by number from the listing of all variables (e.g., :loc 2)
  • :inspect (:i) -- Inspect a data structure, meaning enter the ACL inspector tool. Example: :i * will inspect the datum returned by the previous Lisp expression
  • :restart (:rest) -- Restart execution of the function at the current stack frame
  • :return (:ret) -- Cause execution of the function at the current stack frame to return a value that the user will be prompted for next