AutoCAD Tip: VLIDE AutoLISP Debugging Best Practices

Sharpening your AutoLISP debugging skills in VLIDE (Visual LISP Editor) dramatically reduces downtime and improves code quality.

• Create a safe debugging setup
  • Work in a scratch/test DWG to avoid polluting production files.
  • Open VLIDE (command: VLIDE), load your LISP with “Load Active Edit Window,” and save often.
  • Enable “Break on Error” (VLIDE Debug menu) so execution stops exactly where an exception occurs.
  • Use a dedicated support folder added to the AutoCAD Support File Search Path; keep dev files separate from released code.
  • Keep AutoCAD current for the best VLIDE stability; if you need licenses or upgrades, see NOVEDGE.
• Core VLIDE tools that pay off
  • Breakpoints: click the editor gutter to toggle; use Continue/Step Into/Step Over from the Debug toolbar to control flow.
  • Watch/Inspect: right‑click a symbol to add it to the Watch window, or Inspect any expression while paused.
  • Evaluate on the fly: use the Console (Command Window in VLIDE) to test small expressions without rerunning the whole routine.
  • Balance and format: “Check Text in Editor” and parentheses matching quickly reveal missing parens or stray quotes.
  • Reload fast: use “Load Active Edit Window” after each change to retest immediately.
• Robust error handling patterns
  • Localize an error handler inside commands to guarantee cleanup.

  (defun c:Demo (/ *error* oldsnap)
    (defun *error* (msg)
      (if (and msg (not (wcmatch (strcase msg) "*BREAK*,*CANCEL*,*EXIT*")))
        (princ (strcat "\nError: " msg)))
      (if oldsnap (setvar 'OSMODE oldsnap))
      (princ))
    (setq oldsnap (getvar 'OSMODE))
    (setvar 'OSMODE 0)
    ;; ... your code here ...
    (*error* nil))

  • Wrap risky calls with Visual LISP’s exception helpers:

    (setq res (vl-catch-all-apply 'some-func some-args))
    (if (vl-catch-all-error-p res)
      (princ (strcat "\nCaught: " (vl-catch-all-error-message res))))

• Logging and timing for evidence‑based fixes
  • Append to a log file during runs:

    (setq f (open "C:/Temp/demo.log" "a"))
    (write-line (strcat (menucmd "M=$(edtime,0,YYYY-MM-DD HH:MM:SS)") " - step A") f)
    (close f)

  • Rough profiling via MILLISECS:

    (setq t0 (getvar "MILLISECS"))
    ;; ... work ...
    (princ (strcat "\nms: " (itoa (- (getvar "MILLISECS") t0))))

• Autoload and namespace hygiene
  • Defer loading until the user calls the command (keeps startup fast):

    (defun c:MyCmd () (if (not (findfile "mytools.lsp")) (princ))
      (load "mytools" -1) (c:MyCmd))

  • Prefix your functions (e.g., acme:) and localize variables with the defun slash list or let to avoid leaks and collisions.
  • For deployment and subscriptions, check NOVEDGE’s AutoCAD solutions.
• Clean state between tests
  • Remove test reactors: (vlr-remove-all) before re‑running.
  • Restore any system variables you changed; make restoration part of your error handler.
  • Force a garbage collection with (gc) to catch lifetime issues early.
• Practical workflow tips
  • Keep code, DCL, and resources under version control; tag stable builds.
  • Use eTransmit to share test packages with peers; for teams and add‑ons, explore NOVEDGE for tooling and licensing.

With disciplined VLIDE use, targeted logging, and defensive error handling, you’ll locate faults faster, ship sturdier routines, and spend more time designing than debugging.