Copyright © 1991, 1992 Daniel LaLiberte
This is edition 1.2 of the Edebug User Manual for edebug Version 2.6, February 1991.
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 this author.
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Edebug is a source level debugger for GNU Emacs Lisp that provides the following features:
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.
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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
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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.
(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
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
(see section 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 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
(see section 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; see section 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 Miscellaneous).
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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 defuns (and
defmacros) are evaluated with edebug-defun.
eval-region is redefined to use edebug-defun when
evaluating defuns (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 Evaluation for discussion of other evaluation functions available inside of edebug.
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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.
(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. See section 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 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.)
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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 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 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.
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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 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.)
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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 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.
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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 (see section 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 (see section 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.)
(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.
(edebug-eval-print-last-sexp) Similar to eval-print-last-sexp
but in the outside context.
(edebug-eval-last-sexp) Similar to eval-last-sexp but in the
outside context.
(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.
(edebug-delete-eval-item) Delete the evaluation list group that
point is in.
(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 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 (see section The Outside Context). One way to
observe the difference is to look at the recursion-depth.
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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.
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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 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.
| 1.10.1 Just Checking | ||
| 1.10.2 Outside Window Configuration | ||
| 1.10.3 Recursive Edit | ||
| 1.10.4 Side Effects |
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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.
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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.
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.
edebug-save-displayed-buffer-points is non-nil. See the
description of that variable for more details.
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.
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If edebug stops execution and enters a recursive-edit, the following additional things are saved and restored.
match-data so that it works
better with string-search.
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??).
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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:
max-lisp-eval-depth and max-specpdl-size, are also
increased proportionally.
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.
command-history. This is probably recoverable, but I
havent investigated it yet.
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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-specs 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:
symbolpAn unevaluated symbol.
integerpAn unevaluated number.
stringpAn unevaluated string.
vectorpAn unevaluated vector.
atomAn unevaluated number, string, symbol, or vector.
sexpAn unevaluated sexp (atom or list); the argument may be nil or
() but it must not be missing.
formAn evaluated sexp.
functionA 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.
otherAny 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.
&optionalAll 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 [...].
&restAll 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
[...].
&orEach 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?
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Default nil. If non-nil, all defuns and
defmacros evaluated will use edebug. eval-defun without
prefix arg and eval-region will use edebug-defun.
If nil, eval-region evaluates normally, but
eval-defun with prefix arg uses edebug-defun.
eval-region is called by eval-defun,
eval-last-sexp, and eval-print-last-sexp.
You may wish to make this variable local to each elisp buffer by calling
(make-local-variable 'edebug-all-defuns) in your
emacs-lisp-mode-hook. You can use the function
edebug-all-defuns to toggle its value.
Default nil. If non-nil, edebug will assume that all
macro call arguments for macros that have no edebug-form-spec may
be evaluated, otherwise it will not. To specify exceptions for macros
that have some arguments evaluated and some not, you should specify an
edebug-form-spec (see section Macro Calls).
Default nil.
Non-nil causes edebug to stop before symbols as well as after.
This option is used when the edebug-defun is called, not
when edebugging, so set the option before using edebug-defun.
Default t.
If non-nil, save and restore window configuration on edebug calls.
It takes some time to save and restore, so if your program does not care
what happens to the window configurations, it is better to set this
variable to nil.
Default t. If non-nil, save and restore the point and
mark in source code buffers.
Default nil. If non-nil, save and restore the points of
all buffers, displayed or not.
Saving and restoring buffer points is necessary if you are debugging code that changes the point of a buffer which is displayed in a non-selected window. If edebug or the user then selects the window, the buffer’s point will be changed to the window’s point.
Saving and restoring is an expensive operation since it visits each window and each displayed buffer twice for each edebug call, so it is best to avoid it if you can.
Default 'step.
Global initial mode for edebug, if non-nil. This is used when
edebug is first entered for each recursive-edit level. Possible values
are nil (meaning use the current edebug-mode), 'step,
'go, 'Go-nonstop, 'trace, 'Trace-fast,
'continue, and 'Continue-fast.
Default nil. Non-nil if edebug should show a trace of
function entry and exit. Tracing output is displayed in a buffer named
‘*edebug-trace*’, one function entry or exit per line, indented by
the recursion level. You can customize by replacing functions
edebug-print-trace-entry and edebug-print-trace-exit.
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Send me your suggestions and priorities.
If you are interested in running edebug on functions in edebug.el, I find it easiest to first copy edebug.el into another file, say fdebug.el, and replace all strings "edebug" with "fdebug", then evaluate the fdebug buffer and run edebug on functions in fdebug.el.
eval-current-buffer, and perhaps others.
edebug-defun. For now, be sure there is a space before '
and don’t use "" inside strings.
max-lisp-eval-depth and max-specpdl-size
should be set.
overlay-arrow-position and -string be buffer local?
current-local-map instead of emacs-lisp-mode-map
(but only copy the first time after lower level command - to save time).
inhibit-quit while edebugging?
sit-for 0 or 1 in the outside window configuration
between each edebug step.
Maybe it should be a separate option that applies to trace as well.
sit-for time. Less than a second would be nice.
edebug-defun.
Restore to no edebug version after having entered.
Partially implemented with i command.
let,
condition-case, function and macro calls) to view values at that
frame. What about buffer local variables? This is very complex, and
it would be better to have access to the Lisp stack.
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