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trace (AutoLISP)

Aids in AutoLISP debugging

Supported Platforms: Windows, Mac OS, and Web

Signature

(trace [function ...])
function

Type: Symbol

A symbol that names a function. If no argument is supplied, trace has no effect.

Return Values

Type: Symbol or nil

The last function name passed to trace. If no argument is supplied, trace returns nil.

Remarks

The trace function sets the trace flag for the specified functions. Each time a specified function is evaluated, a trace display appears showing the entry of the function (indented to the level of calling depth) and prints the result of the function.

Trace output is sent one of the following locations

  • AutoCAD Command Line window; when Visual LISP is not active in AutoCAD on Windows
  • Visual LISP Trace window (Not available in AutoCAD LT for Windows, or on Mac OS and Web)
Note: Once you start Visual LISP during an AutoCAD session, it remains active until you exit AutoCAD. Therefore, all trace output prints in the Visual LISP Trace window for the remainder of that AutoCAD session. Exiting or closing Visual LISP while AutoCAD is running only closes the IDE windows and places Visual LISP in a quiescent state; it does not result in a true shutdown. You must reopen Visual LISP to view the output in the Trace window.

Use untrace to turn off the trace flag.

Examples

Define a function named foo and set the trace flag for the function: 

(defun foo (x) (if (> x 0) (foo (1- x))))
FOO

(trace foo)
FOO

Invoke foo and observe the results: 

(foo 3)
Entering (FOO 3)
Entering (FOO 2)
Entering (FOO 1)
Entering (FOO 0)
Result: nil
Result: nil
Result: nil
Result: nil

Clear the trace flag by invoking untrace: 

(untrace foo)
FOO

Related Concepts

Related Reference

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