:zoom

Arguments: &key from-read-eval-print-loop brief moderate verbose top bottom count specials function relative all

This command prints the evaluation stack. It uses the current stack frame as the center of attention, and prints some number of frames on either side of the current frame. The value of the variable *zoom-display* is the total number of frames to display, and an equal number of frames are printed above and below the current stack frame, if possible. The arguments to the :zoom command control the type and quantity of the displayed stack.

After a :zoom or any of its analogs (such as :top or :bottom) the special variable cl:* contains the lisp expression representing the current frame. That expression is approximately what is shown in a moderate display with :function nil, regardless of the mode in which :zoom itself displays.

The from-read-eval-print-loop argument controls whether frames after the most recent entry to the Lisp read-eval-print-loop are ignored (when this argument is true, the default) or not (when this argument is nil). This argument should be specified nil when :zoom is called programmatically. It should be left t when :zoom is called interactively.

The remaining keyword arguments to :zoom are described in the following table.

:zoom Keyword Arguments
:zoom keyword	Functionality	Keyword argument value
		nil	non-nil
`:brief`	These control the amount of information :zoom prints. Specify only one at a time. Chosen value sticks from one call of :zoom to the next. See examples of the output styles in :brief, :moderate, and :verbose modes of :zoom in debugging.htm.	`:moderate` is used.	:zoom will print the function names of the stack frames only. Frames will be separated by `<-' and more than one will appear on a line. The current frame will be displayed specially.
`:moderate`		has no effect on mode of the display	:zoom will print function names and actual parameters. :moderate is the initial default display mode.
`:verbose`		`:moderate` is used	:zoom will print function names, formals (the names of the parameters in the function definition) and actual parameters.
`:top`	These arguments control where :zoom places the current stack frame pointer. Specify only one at a time.	has no effect.	current stack frame pointer will be at the top of the stack.
`:bottom`		has no effect.	current stack frame pointer will be at the bottom of the stack.
`:count`	Integer number of frames to print. Initial default value is controlled by `zoom-display`. Specifying a value sets that variable so the value sticks.	Not applicable.	The value t (but not other true values) means display all applicable frames.
`:specials`	If specified, sets (not binds) the value of `zoom-print-special-bindings`. The value of this argument sticks between :zooms.	Specials bound by active functions will not be printed.	If `zoom-print-special-bindings` is true, :zoom will print any specials bound by active functions.
`:function`	Affects how frames are printed. The value of this arguments sticks from one call of :zoom to another.	Frames will be printed as (funcall #<function . . .> . . .).	Frames will be printed as (foo . . .). This is the initial default.
`:relative`	Print line numbers relative to the current frame for :moderate and :verbose :zoom displays (has no effect on :brief display). The value of this argument sticks from one call of :zoom to the next.	Do not print relative identifiers. This is the initial default.	An identifier is printed on each line output giving the location of that line relative to the current frame.
`:all`	Provides override to the :hide command. `:all` differs from the command :unhide in the following way. :unhide (called with no arguments) reverts the list of hidden frames to the original list of hidden frames. Specifying the `:all` argument as true causes all frames to be displayed. The value of this argument sticks from one call of :zoom to another.	If specified and `nil`, the frames specified by :hide will be hidden. This is the initial default.	If specified and true, then the list associated with the :hide command is ignored and all frames are displayed.
`:length`	Bind the value of `zoom-print-length` to the specified value when printing the backtrace. This argument is not sticky, that is it does not affect that value of `zoom-print-level`.	Place no restrictions on the length of data printed in a frame. Note that in some cases, very long lists are printed, making reading the backtrace difficult. If that happens call :zoom again with a numeric value for this argument (or with this argument unspecified so the value of `zoom-print-length` is used).	The value should be a postive integer. `zoom-print-length` will be bound to this value while the output is printed.
`:level`	Bind the value of `zoom-print-level` to the specified value when printing the backtrace. This argument is not sticky, that is it does not affect that value of `zoom-print-level`.	Place no restrictions on the level (depth within lists) of data printed in a frame.	The value should be a postive integer. `zoom-print-level` will be bound to this value while the output is printed.

:zoom and the Debug window in the IDE on Windows

The Debug window in the Integrated Development Environment, supplied with Allegro CL on Windows, also provides a view of the stack similar to :zoom. See the description of the Debug Windows after an error for details. Note that these two views (that in the Debug window and that displayed by :zoom) are independent, meaning each view controls how it is displayed (for example, whether hidden frames are shown or left out, how many frames are shown, etc.) independently from the other.

See top-level.htm for more information on top-level commands. See debugging.htm for information on the debugger and examples of tracing.