The CICA Windows Explosion!/The CICA Windows Explosion! - Disc 2.iso/demo/wemdemo4.zip/INFO/EDEBUG.1

GNU Info File | 1994-09-21 | 49KB | 842 lines

This is Info file ../info/edebug, produced by Makeinfo-1.56 from the
input file edebug.txi.
   This file documents Edebug
   This is edition 1.2 of the Edebug User Manual for edebug Version 2.6,
   Copyright (C) 1991 Daniel LaLiberte
   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.
File: edebug,  Node: Top,  Next: Installation,  Up: (dir)
Edebug
******
* Menu:
* Installation::        Installation
* Using Edebug::        Using Edebug
* Evaluating defuns::        Evaluating defuns
* Edebug Modes::        Edebug Modes
* Miscellaneous::        Miscellaneous
* Breakpoints::            Breakpoints
* Views::            Views
* Evaluation::            Evaluation
* Printing::            Printing
* The Outside Context::        The Outside Context
* Macro Calls::            Macro Calls
* Options::            Options
* Todo List::            Todo List
* Index::            Index
   Edebug is a source level debugger for GNU Emacs Lisp that provides
the following features:
   * Step through the evaluation of your functions and macros, stopping
     before and after each expression, displaying the results of
     expressions.
   * Set conditional or unconditional breakpoints.
   * Go until a breakpoint is reached, or ignore breakpoints.
   * Trace slow or fast stopping briefly at each stop point, or each
     breakpoint.
   * Evaluate expressions as if outside of edebug.
   * Automatically reevaluate a list of expressions and display their
     results each time edebug updates the display.
   * Output tracing info on function enter and exit.
   * Catch errors normally caught by debug.
   * Display backtrace without edebug calls.
   * Interface with the `custom-print' package.
   It isn't necessary to read all of this document, or even most of it,
in order to make use of edebug.  You should minimally read sections
Installation, Using Edebug, and Edebug Modes; the rest can be read as
needed.
   This manual assumes you are familiar with Emacs Lisp, as described
in the GNU Emacs Lisp Reference Manual.  You might want to review the
chapters on Evaluation and Debugging.
File: edebug,  Node: Installation,  Next: Using Edebug,  Prev: Top,  Up: Top
Installation
============
   Put `edebug.el' in some directory in your `load-path' and
byte-compile it.
   Put the following forms in your `.emacs' file.
     (define-key emacs-lisp-mode-map "\C-xx" 'edebug-defun)
     (autoload 'edebug-defun "edebug")
   If you wish to change the default edebug global command prefix,
include the following.
     (setq edebug-global-prefix "\C-xX") ; or whatever you want
File: edebug,  Node: Using Edebug,  Next: Evaluating defuns,  Prev: Installation,  Up: Top
Using Edebug
============
   To use edebug you must be editing an Emacs Lisp buffer using
`emacs-lisp-mode', or its equivalent, since the Emacs Lisp syntax table
must be present.
   The following commands are described in this section.
`C-xx'
     (`edebug-defun') Evaluates the function or macro at or after point
     setting it up for use by edebug.  Unlike `eval-defun' it always
     prints `edebug: NAME' in the minibuffer and a prefix argument has
     a different effect as described below.  If a syntax error is
     found, point is left at the error and mark is set to the original
     point.
     (`edebug-help') Display the help message for `edebug-mode'.
     (`abort-recursive-edit') Abort the edebug recursive edit.  This
     only aborts one level as opposed to all the way to the top level.
     (`top-level') Exit all recursive editing levels to the top level
     command loop.
     (`edebug-previous-result') Redisplay the result of the previous
     expression in the echo area.
   To use edebug, simply evaluate a `defun' or `defmacro' with
`edebug-defun' (`C-xx') when the point is in or before the definition.
The next time your function or macro is called, edebug will be called.
From now on, discussion about using edebug with functions includes
macros, unless otherwise specified.  Like `eval-defun', `edebug-defun'
evaluates function definitions, but adds edebug calls to the lambda
expression.
   To restore a function to normal operation after the definition has
been evaluated with `edebug-defun', simply reevaluate it with one of the
commands that evaluate definitions (e.g., `eval-defun' (`M-C-x'),
`eval-current-buffer', or if the buffer is unchanged, `load-library').
However, the behavior of most of these evaluating functions can also be
modified by edebug, as described in *Note Evaluating defuns::.
   Implementation note:  Recall that a `defun' is the source code
definition of a function and evaluation of a definition puts the lambda
expression for the function in the function cell of the symbol naming
the function.  After evaluating a `defun' with `edebug-defun', the
lambda expression stored in the function symbol's function cell
contains a call to the function `edebug-enter' at the top level and
individual calls to the function `edebug-before' and `edebug-after' for
each expression that may be evaluated in the function.
   When you call your function explicitly or via another function,
edebug will be called, but it may or may not stop execution depending
on what the current edebug mode is.  Some edebug modes only update the
display to indicate the progress of the evaluation without stopping
execution.  The default initial edebug mode is `step' which does stop
execution.  The edebug modes are described in detail below (*note
Edebug Modes::.).
   Each time edebug updates the display to indicate the progress of the
evaluation, the buffer that the function is defined in is displayed
temporarily.  Also point is moved (temporarily) to the expression in the
function about to be evaluated (or just evaluated) and an overlay arrow
is displayed at the left end of the line containing point.  If the point
is not visible in the window, the window start is changed
(semi-permanently!) so that point is visible, while trying to display
as much of the following code as possible.  See *Note The Outside
Context:: for more details on how the Emacs display is affected by
edebug.
   In the example below, the definition of the `fac' function has been
evaluated with `edebug-defun' (by positioning point within the
definition and hitting `C-xx') and the expression `(fac 3)' has been
evaluated.  The arrow on the first line indicates that edebug has been
entered.  To indicate that you are stopped before the first expression,
the cursor would be on the first left parenthesis of that line.
     (defun fac (n)
     =>(if (< 0 n)
           (* n (fac (1- n)))
         1))
   When execution is stopped, you are "in edebug" in a recursive edit
with point in the buffer defining the function, as described above.
This buffer, called the "edebug buffer", is made read-only and the
`edebug-mode' minor mode is activated.  Several commands are available
in addition to the standard `emacs-lisp-mode' bindings.  Try the `?'
command (`edebug-help') for a list of edebug commands.  From the edebug
recursive edit, you are permitted to call functions that invoke edebug
again recursively.  At any time in edebug, you can quit to the top
level with `q' (`top-level)' or abort one recursive edit level with `a'
(`abort-recursive-edit').
   Places within a function that edebug may stop, called "stop points",
are before and after expressions that are not self-evaluating, i.e. list
forms and symbols.  However, edebug does not stop before symbols (i.e.,
variables) unless `edebug-stop-before-symbols' is non-`nil', since it
is not usually useful to do so.  When stopped after an expression,
edebug displays the result of the expression in the minibuffer.  Use
the `r' command (`edebug-previous-result') to see that result again.
You can control the way in which expression results are printed by
using the `custom-print' package (*note Printing::.).
   Edebug knows about all the special forms, interactive forms with
expressions, anonymous lambda expressions, and embedded `defun' or
`defmacro' calls.  It cannot know what a macro will do with the
arguments of a macro call so you must tell it; *note Macro Calls::. for
the details.  You can use the same mechanism to tell edebug that some
function arguments should be functions.
   Continuing the example of the `fac' function, the user may step
through the execution of the function (with SPC) stopping in edebug at
the stop points which are marked with a period:
     (defun fac (n)
     =>.(if .(< 0 n.).
           .(* n. .(fac (1- n.).).).
         1).)
   Whenever a function evaluated with `edebug-defun' is active, the
Emacs debugger named by the variable `debugger' is set to
`edebug-debug', so it is not necessary to set it yourself.  (Currently
there is no option to turn off this feature.)  If an error occurs and
`debug-on-error' is non-`nil', edebug will display the error and move
point to the last known stop point.  This applies to quit signals too,
if `debug-on-quit' is non-`nil'.  But in any case, if no function that
was evaluated with `edebug-defun' is currently active, `debug' is run
normally.  Note that you can also get a full backtrace inside of edebug
(see *Note Miscellaneous::).
File: edebug,  Node: Evaluating defuns,  Next: Edebug Modes,  Prev: Using Edebug,  Up: Top
Evaluating defuns
=================
   There are a couple other ways to evaluate a `defun' for edebug
besides calling `edebug-defun' directly.  The variable
`edebug-all-defuns' affects the behavior of several commands defined by
Emacs.  `eval-defun' (`M-C-x') is redefined by `edebug.el' to use
`edebug-defun' if `edebug-all-defuns' is non-`nil', or alternatively,
if you supply a prefix argument.  But if `edebug-all-defuns' is
non-`nil' and you also supply a prefix argument, `edebug-defun' will
not be used.  In other words, the prefix argument of `eval-defun'
reverses the effect of `edebug-all-defuns'.  The default value of
`edebug-all-defuns' is `nil'.  Call the function `edebug-all-defuns' to
toggle the value of the variable `edebug-all-defuns'.
   Note that this version of `eval-defun' evaluates whatever top level
form it finds, as it normally does, but only `defun's (and `defmacro's)
are evaluated with `edebug-defun'.
   `eval-region' is redefined to use `edebug-defun' when evaluating
`defun's (if `edebug-all-defuns' is non-`nil').  The prefix argument
for `eval-region' has the normal behavior since it is used by other
functions (including the standard functions `eval-defun',
`eval-print-last-sexp', and `eval-last-sexp').  If an error occurs
during the evaluation, point is left after the expression in error.
Also, this `eval-region' does not use `narrow-to-region' to limit the
scope of evaluation, and consequently there is a small difference in
how white space is handled after an expression when the output is
inserted in the buffer.
   `eval-current-buffer' is redefined to use `eval-region', since the
standard version does not, thus gaining all the benefits of the new
`eval-region'.
   Note that loading does not invoke `edebug-defun', since the load
functions are subroutines that use the internal `eval-region' rather
than the redefined one supplied by `edebug.el'.  This could be
considered a feature since loading a file does not also visit the file
which would be necessary if edebug were to be invoked on one of the
functions defined in the file.
   See *Note Evaluation:: for discussion of other evaluation functions
available inside of edebug.
File: edebug,  Node: Edebug Modes,  Next: Miscellaneous,  Prev: Evaluating defuns,  Up: Top
Edebug Modes
============
   While your function is being evaluated, edebug is in one of several
modes.  The current mode is called the "edebug mode", not to be
confused with major or minor modes.  The current edebug mode determines
how edebug displays the progress of the evaluation, whether it stops at
each stop point, or continues to the next breakpoint, for example.
   Each time you enter edebug, you will be in the same mode you
specified the previous time you were in edebug.  The exception is when
edebug is first entered for each recursive edit level; then the mode is
changed to the value in the global variable `edebug-initial-mode', which
defaults to "step" mode.  In the case of a command where the
`interactive' form has an expression argument, the expression is
evaluated before the function is really entered, so the edebug mode
defaults to `edebug-initial-mode' both for this expression and for the
first expression in the function body.  (In fact, this repeated
resetting to the initial mode also occurs each time your function is
called non-recursively before returning to the command level which
invoked the function.)
   Below is a table of the keys which change the edebug mode.  For each
key, the mode is set and the recursive edit is exited; what happens
next depends on which mode you selected, which code your function
executes, and whether a breakpoint is hit.  You can also set the edebug
mode when edebug is not running (or in a non-edebug buffer) by hitting
`C-xX' (default value of `edebug-global-prefix') followed by the same
key as used inside of edebug.  Most of the other edebug commands are
available in the same manner.
`SPC'
     (`edebug-step-through') Step mode stops at the next stop point
     encountered.
     (`edebug-trace') Trace mode pauses one second at each edebug stop
     point.
     (`edebug-Trace-fast') Trace with zero pause time at each stop
     point.
     (`edebug-continue') Continue after pausing for one second at each
     breakpoint.
     (`edebug-Continue-fast') Continue with zero pause time at each
     breakpoint.
     (`edebug-go') Go until a breakpoint.  *Note Breakpoints::.
     (`edebug-Go-nonstop') Go non-stop ignoring breakpoints.  This is
     the fastest way to execute code that has edebug calls in it, but
     this mode of execution is still interruptible; see below.
     (`edebug-stop') Stop executing at the first stop point encountered,
     regardless of the mode.  This command does not change the mode and
     does not continue execution; it is intended to be used to
     interrupt execution.
   To execute edebugged code more rapidly, use commands farther down in
the list.  For example, Go-nonstop mode is alot faster that trace mode
since it ignores breakpoints.  The continue modes do not stop at
breakpoints, but merely pause at them.
   While executing or tracing, you can interrupt the execution by
hitting one of the edebug command characters, at which time the command
is acted on.  For example, hitting SPC will stop execution at the first
stop point because input is pending, but will then step to the next stop
point.  Alternatively, `S' is bound to `edebug-stop' which does nothing
but stop.  If your function happens to read input, a character you hit
intending to interrupt execution may be read by the function instead,
so be careful in the neighborhood of the read call.  Also see the
discussion of errors and quit signals in *Note Using Edebug::.
   Keyboard macros invoked within edebug will not work across edebug
calls, so you must enter each edebug command separately.  (It doesn't
seem worth it to save and restore keyboard macro definitions and
executions between calls to edebug in such a way that it doesn't affect
any outside command processing, and it may not be possible in any case.)
File: edebug,  Node: Miscellaneous,  Next: Breakpoints,  Prev: Edebug Modes,  Up: Top
Miscellaneous
=============
   Some miscellaneous commands are described here.
     (`edebug-forward-sexp') Proceed from the current point to the sexp
     found by first doing `forward-sexp' and then switching to go mode.
     If a prefix argument is supplied, do `forward-sexp' that many
     times.  If there are not enough sexps for `forward-sexp', call
     `edebug-step-out' instead.  Be careful that the sexp found by
     `forward-exp' will be executed; this will not always be the case in
     a `condition-case', for example.  A temporary breakpoint is set at
     the stop point, so it will be used and cleared whenever execution
     reaches it.  See *Note Breakpoints:: for the details on
     breakpoints.
     Notice that we do the `forward-sexp' starting at the current point
     rather than the stop point, thus providing more flexibility.  If
     you want to start the search at the stop point, first do
     `edebug-where' (`w').
     (`edebug-step-out') Proceed from the current point to the end of
     the containing sexp.  If the containing sexp is the top level
     defun, go to the end of the last sexp instead, or if that is the
     same point, then step out of the function.  Therefore this command
     does not exit the currently executing function unless you are
     positioned after the last sexp of the function.
     Like `edebug-forward-sexp', this command switches to go mode to get
     to the containing sexp.  The only situation in which the
     containing sexp will not be reached by edebug is if a non-local
     exit by-passes it.
     (`edebug-step-in') Step into the function about to be called.  Use
     this command before any of the arguments of the function call are
     evaluated since otherwise it will be too late.  One side effect of
     using `edebug-step-in' is that the next time the stepped-into
     function is called, edebug will be called there as well.  (I may
     try to fix this in the future.)
     (`edebug-goto-here') Proceed to the stop point near the current
     point.  A temporary breakpoint is used.  See *Note Breakpoints::
     for details on how the stop point is found.
     (`edebug-backtrace') A `debug'-like backtrace is displayed.  All
     calls to edebug functions are removed to clean up the display.
     This backtrace does not function like the standard backtrace so
     you cannot specify which frames to stop at, etc. - but it is
     better than nothing.  The backtrace buffer is killed automatically
     when you continue execution.
File: edebug,  Node: Breakpoints,  Next: Views,  Prev: Miscellaneous,  Up: Top
Breakpoints
===========
   The purpose of "breakpoints" is to let you specify significant
places in your code where you would like edebug to stop or pause
execution.  Breakpoints may be set at any stop points as defined in
*Note Using Edebug::, even before symbols.  Edebug will stop or pause
at a breakpoint except when the edebug mode is Go-nonstop.  For setting
and unsetting breakpoints, the stop point that is affected is at or
after the current point.  The following commands are related to
breakpoints:
     (`edebug-set-breakpoint') Set a breakpoint at the stop point at or
     after the current point.  With prefix-arg, the breakpoint is
     temporary.
     (`edebug-unset-breakpoint') Unset or clear a breakpoint at the
     stop point at or after the current point.
     (`edebug-set-conditional-breakpoint') Set a conditional
     breakpoint.  You are asked for the conditional expression.  With
     prefix-arg, the breakpoint is temporary.
     (`edebug-next-breakpoint') Move point to the next breakpoint in
     the current function definition.
   While in edebug, you can set a breakpoint with `b'
(`edebug-set-breakpoint') and unset (or clear) it with `u'
(`edebug-unset-breakpoint').  First move point to a position at or
before the desired edebug stop point, then hit the key to change the
breakpoint.  Unsetting a breakpoint that has not been set does nothing.
   Reevaluating the defun with `edebug-defun' clears all breakpoints in
the function.  (Let me know if you would like breakpoints preserved; I
could use marks for breakpoints instead of relying on the offsets from
the beginning of the defun.)
   A "conditional breakpoint" is set with `x'
(`edebug-set-conditional-breakpoint').  When you set a conditional
breakpoint you will be asked for an expression which is evaluated each
time the breakpoint is reached.  Edebug will only stop at a conditional
breakpoint if the condition evaluates to non-`nil'.  But conditional
breakpoints are not even checked if the edebug mode is Go-nonstop.
   For both conditional and unconditional breakpoints, the breakpoint
can be made into a "temporary breakpoint" if you give a prefix arg to
the command.  After breaking at a temporary breakpoint, it is
automatically cleared.
   To find out where your breakpoints are, use the `B'
(`edebug-next-breakpoint') command which moves point to the next
breakpoint in the function following point, or to the first breakpoint
if there are no following breakpoints.  (Note that this command does not
continue execution - it just moves the point.)
File: edebug,  Node: Views,  Next: Evaluation,  Prev: Breakpoints,  Up: Top
Views
=====
   If the function you are debugging modifies the Emacs window
environment, you may wish to check the "outside window configuration"
as it was before edebug was called, since edebug itself also modifies
the window environment (see *Note Outside Window Configuration:: for
how edebug tries to restore it). The following commands relate to views
in general.
     (`edebug-view-outside') View the outside window configuration.
     (`edebug-bounce-point') Bounce to the point in the outside current
     buffer, and return after one second.
     (`edebug-where') Move point back to the current stop point.
     (`edebug-toggle-save-windows') Toggle the `edebug-save-windows'
     variable.  Each time you toggle it, the inside and outside window
     configurations become the same as the current configuration.  By
     turning this off and on again, edebug thereafter restores the
     outside window configuration to the current configuration.
   You can view the outside window configuration with `v'
(`edebug-view-outside') or bounce to the current point in the current
buffer with `p' (`edebug-bounce-point'), even if it is not normally
displayed.  After moving point or changing buffers, you may wish to pop
back to the stop point with `w' (`edebug-where') from an edebug window
or `C-xXw' in any window.
File: edebug,  Node: Evaluation,  Next: Printing,  Prev: Views,  Up: Top
Evaluation
==========
   This section describes commands related to the explicit and automatic
evaluation of expressions in edebug.  Edebug attempts to make such
evaluations while inside of edebug appear that they are occuring
outside of edebug, as if edebug had not been invoked.  Almost everything
about the outside context is restored (*note The Outside Context::. for
the details).  But `M-ESC' (`eval-expression') still evaluates
expressions normally (in the current context) since that is occasionally
needed.  Also supported is an evaluation list window where expressions
may be evaluated interactively or automatically.
   You can control the way in which expression results are printed by
using the `custom-print' package (*note Printing::.).
     (`edebug-eval-expression') Evaluates an expression in the "outside
     context" of your function, rather than in the edebug context as
     `M-ESC' does.  (These commands are therefore consistent with the
     same commands in the standard debugger.)
`C-xC-e'
     (`edebug-eval-last-sexp') Like `eval-last-sexp' except in the
     outside context.
     (`edebug-visit-eval-list') Jump to an evaluation list window in
     which several other commands apply, described below.  The
     evaluation list is reevaluated each time the edebug display is
     updated (including tracing) and the results are displayed in a
     temporary buffer `*edebug*'.
   The following commands apply to the evaluation list which is
displayed in the `*edebug*' buffer.  All the `lisp-interaction-mode'
commands are also available.
`LFD'
     (`edebug-eval-print-last-sexp') Similar to `eval-print-last-sexp'
     but in the outside context.
`C-xC-e'
     (`edebug-eval-last-sexp') Similar to `eval-last-sexp' but in the
     outside context.
`C-cC-u'
     (`edebug-update-eval-list') Build a new evaluation list from the
     first expression of each group, reevaluate and redisplay.  Groups
     are separated by a line starting with a comment.
`C-cC-d'
     (`edebug-delete-eval-item') Delete the evaluation list group that
     point is in.
`C-cC-w'
     (`edebug-where') Jump back to the edebug buffer at the current stop
     point.
   In the evaluation list window, type in expressions and evaluate them
with `LFD' (`edebug-eval-print-last-sexp') or `C-xC-e'
(`edebug-eval-last-sexp'), just as you would for lisp interaction mode
but the evaluation is done in the outside context.  (Note:
`eval-region' is not redefined to evaluate in the outside context; it
is only redefined to use `edebug-defun' when it encounters a defun -
see *Note Evaluating defuns::.)
   The expressions you enter interactively, and their results, will be
lost when you continue execution of your function unless you add them
to the evaluation list.  To add any number of expressions to the
evaluation list use `C-cC-u' (`edebug-update-eval-list').  This builds a
new list from the first expression of each "group", where groups are
separated by a line starting with a comment.
   When the evaluation list is redisplayed, each expression is displayed
followed by the result of evaluating it, and a comment line.  If an
error occurs during an evaluation, the error message is displayed in a
string as if it were the result.  Therefore expressions that use
undefined variables will not interrupt your debugging.  Here is an
example of what the evaluation list window looks like after several
expressions have been added to it.
     (current-buffer)
     #<buffer *scratch*>
     ;---------------------------------------------------------------
     (point-min)
     1
     ;---------------------------------------------------------------
     (point-max)
     2
     ;---------------------------------------------------------------
     edebug-outside-point-max
     "Symbol's value as variable is void: edebug-outside-point-max"
     ;---------------------------------------------------------------
     (recursion-depth)
     0
     ;---------------------------------------------------------------
     this-command
     eval-last-sexp
     ;---------------------------------------------------------------
   You can delete the group that point is positioned in with `C-cC-d'
(`edebug-delete-eval-item'), or use normal editing commands to modify
the text as much as you want (e.g. delete-region).  Be sure to update
the evaluation list with `C-cC-u' before you continue evaluation of
your function or quit to the top level, unless you want your changes to
be lost.  Also be sure to separate each "group" with a comment before
updating, otherwise the wrong expressions may end up in the list.
   You can return to the source code buffer (the edebug buffer) with
`C-cC-w' which is equivalent to `C-xXw'.  The `*edebug*' buffer is
killed when you continue execution of your function, and recreated next
time it is needed.
   If you are concerned with exactly how the evaluation is done, you may
need to know that the evaluation of expressions occurs in one of two
slightly different outside contexts.  If the evaluation list is
non-empty when edebug is entered, the context used to evaluate it is
closest to the true outside context since nothing much has changed when
the evaluation is done.  However, when you evaluate expressions within
edebug using the above described interactive commands or when you update
the evaluation list, as much of the outside context is restored as
possible, but not everything (*note The Outside Context::.).  One way to
observe the difference is to look at the `recursion-depth'.
File: edebug,  Node: Printing,  Next: The Outside Context,  Prev: Evaluation,  Up: Top
Printing
========
   If the results of your expressions contain circular references to
other parts of the same structure, the standard Emacs print subroutines
may fail to print with an error, "Apparently circular structure being
printed".  If you only use cdr circular lists (where cdrs of lists point
back; what is the right term here?), you can limit the length of
printing with `print-length' and edebug does this for you when printing
out the previous result.  But car circular lists and circular vectors
generate the above mentioned untrappable error in Emacs version 18.
Version 19 will support `print-level', but it is often useful to get a
better print representation of circular structures.
   To handle printing of structures more generally, you can use the
`custom-print' package which supports `print-level', `print-circle',
and further customizations via `custom-print-list' and
`custom-print-vector'.  See the documentation strings of these
variables for more details.  There are two main ways to use this
package.  First, you may replace `prin1', `princ', and some subroutines
that use them by calling `install-custom-print-funcs' so that any use
of these functions in lisp code will be affected.  Second, you could
call the custom routines directly, thus only affecting the printing
that requires them.  Edebug uses the second method, as described next.
   To load the package and activate custom printing only for edebug,
simply use the command `edebug-install-custom-print-funcs'.  This sets
the function cells of `edebug-prin1', `edebug-print',
`edebug-prin1-to-string', and `edebug-format' to the symbol names of
the corresponding custom versions.  Therefore, any changes you make to
the custom functions or to the variables controlling custom printing
take effect immediately.  Notice you still need to set `print-level' or
`print-circle'.  To restore the standard print functions, use
`edebug-reset-print-funcs'.
File: edebug,  Node: The Outside Context,  Next: Macro Calls,  Prev: Printing,  Up: Top
The Outside Context
===================
   This section is useful for those who need to know more precisely what
edebug is doing that might affect editing and the context of expression
evaluation.  For the most part, edebug operates transparently and there
should be no apparent difference running with edebug, except for
debugging itself.  If you find any variation with what is described
here, please let me know.
   An important distinction is made between the "outside context" which
exists before edebug is invoked, and the "inside context" which exists
while edebug is active.  Most of the outside context is saved and
restored each time you enter and exit from edebug.  In addition, most
evaluations you do within edebug (see *Note Evaluation::) occur in the
same outside context which is temporarily restored for the evaluation.
   Described in this section are the aspects of the outside context that
are saved and restored including things as diverse as window
configurations, current buffer status, and variable values.  These
aspects are divided into three sections, corresponding to the degree to
which edebug has affected the outside context.  The first section,
immediately following this, is for those things that are affected any
time edebug is called even if the display is not updated.  The second
section is for when edebug must update the display.  The third section
is for when edebug stops execution and enters a recursive edit.
Finally, the few unavoidable side effects of using edebug are described.
* Menu:
* Just Checking::        Just Checking
* Outside Window Configuration::  Outside Window Configuration
* Recursive Edit::        Recursive Edit
* Side Effects::        Side Effects
File: edebug,  Node: Just Checking,  Next: Outside Window Configuration,  Prev: The Outside Context,  Up: The Outside Context
Just Checking
-------------
   The following are saved and restored when edebug is called even if
the display is not updated.  One reason there is anything at all to
save and restore is that the call to `edebug-enter' must remain active
while your function is active, and this impacts the Lisp stack.  The
other reason is that execution may be interrupted at any time unless the
edebug mode is Go-nonstop, but an executing keyboard macro should not
interrupt execution.
   * `max-lisp-eval-depth' and `max-specpdl-size' are both incremented
     for each `edebug-enter' call so that your code should not be
     impacted by edebug frames on the stack.  I believe they are
     incremented too much currently, but that is better than not enough.
   * A keyboard macro executed outside of edebug should not affect the
     operation of edebug.  Other input will be caught by edebug,
     however, interrupting execution as described in *Note Edebug
     Modes::.  If you are defining a keyboard macro when edebug is
     entered, all your command input will be included in the macro, but
     this is not much use since the macro will not be executed the same
     way.  I don't know if it is safe to suspend definition of a
     kbd-macro, or if it is useful to allow execution of a macro to
     continue into edebug.  Let me know if you figure this out.
File: edebug,  Node: Outside Window Configuration,  Next: Recursive Edit,  Prev: Just Checking,  Up: The Outside Context
Outside Window Configuration
----------------------------
   One important aspect of the outside context is the "outside window
configuration".  A full description of window configurations may be
found in the GNU Emacs Lisp Reference Manual.  If you are running
`epoch', the concept of a window configuration is generalized to
include the set of current screens, though if you create or destroy
screens while in edebug, this effect will not be reversed.
   When you exit from edebug (each time you continue execution, in
fact), the window configuration outside of edebug is restored to what
it was before edebug was entered.  But since Emacs delays screen update
until needed, if you then reenter edebug before a screen update is
required, it will appear that you never left; that is, the outside
window configuration will not be displayed even though it was in
effect.  If your function completes normally, the outside window
configuration will finally be displayed when you return to the command
level, or any time a screen update is forced by some other means (e.g.
`sit-for').
   The window configuration, as defined by Emacs, does not include which
buffer is current or where point and mark are in the current buffer, but
edebug saves and restores these also.  Note that the outside window
configuration restored by edebug may not be fully consistent with the
real outside context since the selected window may not yet have been
displayed but edebug may have forced screen update.
   If the display needs to be updated by edebug, e.g. a trace mode is
active, the following are saved and restored.  However, if an error or
quit signal occurs, some of these are intensionally not restored for
user convenience.
   * The point of the edebug buffer (the one containing the function
     definition) is saved and restored only if the outside current
     buffer is the same as the edebug buffer.  (The point is also not
     restored on error or quit.)
   * The outside window configuration, as described above, is saved and
     restored if `edebug-save-windows' is non-`nil'.  These are not
     restored on error or quit, but the outside selected window is
     reselected even on error or quit in case a `save-excursion' is
     active.  The window start for the edebug buffer is not restored,
     however, so that the next time it is displayed, the window start
     will be in the same position it was last time.
   * The current buffer, and point and mark in the current buffer are
     normally saved and restored even if the current buffer is the same
     as the edebug buffer.  They are not restored on error or quit, but
     in that event the current buffer will be changed to the outside
     selected window's buffer when you return to the command loop, as
     it normally is.
   * The points of all displayed buffers are saved and restored if
     `edebug-save-displayed-buffer-points' is non-`nil'.  See the
     description of that variable for more details.
   * The `overlay-arrow-position' and `overlay-arrow-string' are saved
     and restored.  Since edebug uses these variables, saving and
     restoring also permits recursive use of edebug, or other uses of
     the overlay arrow by the outside context.
   * `cursor-in-echo-area' is locally bound to `nil' so that the cursor
     shows up in the window.
File: edebug,  Node: Recursive Edit,  Next: Side Effects,  Prev: Outside Window Configuration,  Up: The Outside Context
Recursive Edit
--------------
   If edebug stops execution and enters a recursive-edit, the following
additional things are saved and restored.
   * The read-only status of the edebug buffer, since edebug changes it
     to read-only.
   * The current match data, for whichever buffer was current.  Note
     that Emacs 18.56 partially fixed a bug in `match-data' so that it
     works better with `string-search'.
   * The local keymap of the edebug buffer.
   * `last-command', `this-command', `last-command-char', and
     `last-input-char'.  Commands within the recursive edit will not
     affect these variables outside of edebug.
     But note that the result of `(this-command-keys)' and the value of
     `unread-command-char' cannot be protected, as described below.
   * `standard-output' and `standard-input'.  `recursive-edit' locally
     binds these to the default `nil' values (correct??).
File: edebug,  Node: Side Effects,  Prev: Recursive Edit,  Up: The Outside Context
Side Effects
------------
   Many other things may be changed by the user explicitly while in the
edebug recursive edit if they are not protected against change as
described above, and this may be considered a feature in most cases.
However, some possibly undesirable side effects of using edebug remain,
most of which are unavoidable:
   * Changes to the text of buffers are not undone.
   * Lisp stack usage is increased, but the limits,
     `max-lisp-eval-depth' and `max-specpdl-size', are also increased
     proportionally.
   * The key sequence returned by `this-command-keys' is changed by
     executing commands within edebug and there appears to be no way to
     reset the key sequence from Lisp.
   * `unread-command-char' is not protected because its value appears
     to be used even before the command loop is entered by a recursive
     edit.  Thus storing a char in `unread-command-char' always causes
     it to be used for a command in edebug.  I don't know of a
     work-around.
   * Complex commands executed while in edebug are added to the
     `command-history'.  This is probably recoverable, but I havent
     investigated it yet.
   * When you update the evaluation window, the recursion depth will
     appear one deeper than the outside context recursion depth.
   * Horizontal scrolling of the edebug buffer is not recovered.  This
     is probably recoverable, but I havent investigated it yet.
   * If you discover others, please let me know.
File: edebug,  Node: Macro Calls,  Next: Options,  Prev: The Outside Context,  Up: Top
Macro Calls
===========
   This section describes a mechanism you may use to tell edebug how
the arguments of macro calls should be evaluated.  The same mechanism
may be used for special forms and some function calls.
   To edebug your macro calls, you must specify how the arguments may be
evaluated.  In the general case, not all macro arguments will be
evaluated.  But if it so happens that all your macro arguments are
"evaluatable" (i.e. they may eventually be evaluated either explicitly
in the macro body or when the resulting expansion is evaluated), then
you can set the `edebug-eval-macro-args' option to non-`nil'.  On the
other hand, if you don't want any of your macro arguments to be
evaluated by edebug then you can ensure they will not be wrapped in
edebug calls by setting `edebug-eval-macro-args' to `nil' (the default).
   In the more likely case that some macro arguments are to remain
unevaluated (e.g. a symbol) and some may be evaluated, you can specify
an `edebug-form-spec' for each macro.  Implementation note: edebug uses
`edebug-form-spec's for special forms and some function calls as well
as macro calls.  You can do the same, but there is not really much
point, except for functions that take function arguments.
   Use the macro `def-edebug-form-spec' to define a specification for a
function or macro which is stored in the `edebug-form-spec' property of
the symbol naming the function or macro.  The first argument is the
symbol name and the second argument is the specification which may be
one of five kinds of values.  First, if a specification for a symbol is
`nil' or undefined, then depending on the value of
`edebug-eval-macro-args', all the arguments will be treated as
evaluatable (if it's non-`nil') or unevaluatable (if it's `nil').
   If the specification is a quoted function (symbol or lambda
expression), then this function is called to process the arguments of
the calling form.
   As a convenience, `def-edebug-form-spec' may be given `t' or `0' as
its second argument.  If it is `t', then all arguments are treated as
evaluatable; if it is `0' (not `nil'), then all arguments are treated
as unevaluateable.  Implementation note: these values are actually
converted by `def-edebug-form-spec' to the functions `edebug-forms' and
`edebug-sexps' respectively.
   Finally, if the `edebug-form-spec' is a list, then the elements of
the list describe the types of the arguments of a calling form.  The
list is processed left to right, in the same order as the arguments of
the calling form, and the elements constrain the types of corresponding
arguments and specify whether they may be evaluated.  Each element may
be one of the following:
`symbolp'
     An unevaluated symbol.
`integerp'
     An unevaluated number.
`stringp'
     An unevaluated string.
`vectorp'
     An unevaluated vector.
`atom'
     An unevaluated number, string, symbol, or vector.
`sexp'
     An unevaluated sexp (atom or list); the argument may be `nil' or
     `()' but it must not be missing.
`form'
     An evaluated sexp.
`function'
     A function argument may be a quoted (using quote or function)
     symbol or lambda expression or a form (that should evaluate to a
     function or lambda expression).  The body of an anonymous function
     will be treated as evaluateable.
`OTHER'
     Any other symbol should be the name of a function; this function is
     called on the argument as a predicate, and an error is signaled if
     the predicate fails.  You could use this to check whether a
     literal is of a certain custom type.
`(...)'
     A sublist of the same format as the top level, processed
     recursively.  The actual argument must be a list as well.  Special
     case: if the car of the element is quote, the actual argument must
     match the quoted sexp, usually a symbol (see example of `for'
     macro below).
`[...]'
     A sublist of the same format as the top level, processed
     recursively.  It is processed like `(...)' except the matched
     arguments are inserted in-line into the arguments matched by the
     containing list, somewhat analogous to `@,' in backquoted
     expressions.  This may be used for grouping to build complex
     elements out of the primitives provided.
`&optional'
     All following elements in the specification list at this level may
     or may not match arguments; as soon as one does not match,
     processing of the specification list terminates.  To get only one
     specification item to be optional, use `[...]'.
`&rest'
     All following elements in the specification list at this level are
     repeated in order zero or more times.  Allowing more than one
     `&rest' element is an extension of the normal meaning of &rest.
     All the `&rest' elements need not be used in every repetition,
     however.  Only one `&rest' may appear at the same level of a
     specification list, and `&rest' must not be followed by
     `&optional'.  To specify that only some types arguments are to be
     repeated until failure, followed by some other types of arguments,
     use `[...]'.
`&or'
     Each of the following elements in the specification list at this
     level are alternatives, processed left to right until one
     succeeds.  To group two or more list elements as one alternative,
     bracket them in `[...]'.  Only one `&or' may appear in a list, and
     it may not be followed by `&optional' or `&rest'.  One of the
     alternatives must match, unless the `&or' is preceeded by
     `&optional' or `&rest'.
   If a failure to match occurs, this does not necessarily mean a syntax
error will be signalled; instead, "backtracking" will take place until
all alternatives have been exhausted.  `&optional' elements need not
match at all of course, but evenually every element of the argument
list must be matched or an error will be signalled.  Non-optional
elements in the specification unused when the argument list has been
completely matched will also cause backtracking, or ultimately a syntax
error.
   The combination of backtracking, `&optional', `&rest', `&or', and
`[...]' for grouping provides the equivalent of regular expressions.
The `(...)' lists require balanced parentheses, which is the only
context free (finite state with stack) construct supported.  Dotted
pair notation is not yet supported, but let me know if you need it.
   I am considering writing a compiler for `edebug-form-spec' list
forms that would generate elisp code to process arguments the same way
`edebug-interpret-form-spec' now does it but alot faster.  Suggestions
appreciated.
   Here are some examples of using `edebug-form-spec'.  A `let' form
looks like: `(let (BINDINGS ...) FORMS ...)', where each of the
BINDINGS is either a SYMBOL or `(SYMBOL VALUE-FORM)'.  The
`edebug-form-spec' for a `let' form is defined as follows:
     (def-edebug-form-spec let
       '((&rest
         &or symbolp (symbolp &optional form))
        &rest form))
   A `for' loop macro is defined in the GNU Emacs Lisp Reference Manual
(reference needed), and `cl.el' defines `case' and `do' macros.  Here
are their edebug-form-specs.
     (def-edebug-form-spec for
       '(symbolp 'from form 'to form 'do &rest form))

     (def-edebug-form-spec case
       '(form &rest (sexp form)))

     (def-edebug-form-spec do
       '((&rest &or symbolp (symbolp &optional form form))
         (form &rest form)
         &rest body))
   Finally, the functions `mapcar', `mapconcat', `mapatoms', `apply',
and `funcall' all take function arguments, and edebug defines
specifications like the following one for `apply'.
     (def-edebug-form-spec apply '(function &rest form))
   Note that backquote (``') is a macro that results in an expression
that is not necessarily evaluated.  It is often used to simplify the
definition of a macro where the result of the macro call is evaluated,
but edebug does not know when this is the case.  So do not be surprised
when you cannot step through your backquoted code.  23 On the other
hand, one could wrap the backquoted expression in a special function,
say `edebug-`', which would mean that the result of the backquote form
will, in fact, be evaluated.  Then edebug could wrap evaluateable
expressions within the backquoted expression in edebug calls.  Is it
worth it?