9 The Tracer

9.6 The stepper

The stepper can be accessed from the tracer using the :step option, but is also available via the Common Lisp form

(step form)
where form is a form to be stepped and evaluated. It allows you to single-step through the evaluation of the form, stopping at each call.

You can include a call to step inside a tricky definition to invoke the stepper every time the definition is used.

There are a number of optional settings controlled by the keywords listed below. Use :help within the stepper to see a list of the commands available at that time.

:s [n] Stepper command

Step this form, and all of its subforms. The optional argument n must be a positive integer. If supplied, :s is executed n times.

:st Stepper command

Step this form without stepping its subforms.

:su Stepper command

Step up out of this form without stepping its subforms.

:sr Stepper command

Return a value to use for this form.

:sq Stepper command

Quit the current stepper level.

:redo Stepper command

Redo an event in the history list. This is the same as the normal listener :redo command. See Chapter 10, "The Listener", for details.

:get Stepper command

Bind an event from the history list to a variable. This is the same as the normal listener :get command. See Chapter 10, "The Listener", for details.

:help Stepper command

Prints the list of stepper commands available at that time.

:use Stepper command

Replace some element of a form (either a subform or symbol) by another event from the history list, then evaluate it. This is the same as the normal listener :use command. See Chapter 10, "The Listener", for details.

:his Stepper command

Show a list of the last twenty events. This is the same as the normal listener :his command. See Chapter 10, "The Listener", for details.

9.6.1 - Examples
9.6.2 - Printing
9.6.3 - Values

FreeLisp User's Guide - 5 FEB 1996

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