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Edebug is a source-level debugger for XEmacs Lisp programs that provides the following features:
The first three sections of this chapter should tell you enough about Edebug to enable you to use it.
1.1 Using Edebug | Introduction to use of Edebug. | |
1.2 Instrumenting for Edebug | You must first instrument code. | |
1.3 Edebug Execution Modes | Execution modes, stopping more or less often. | |
1.4 Jumping | Commands to jump to a specified place. | |
1.5 Miscellaneous | Miscellaneous commands. | |
1.6 Breakpoints | Setting breakpoints to make the program stop. | |
1.7 Views | Viewing the outside buffer and window status. | |
1.8 Evaluation | Evaluating expressions within Edebug. | |
1.9 Evaluation List Buffer | Automatic expression evaluation. | |
1.10 Printing | Printing circular structure in Edebug. | |
1.11 Coverage Testing | How to test evaluation coverage. | |
1.12 The Outside Context | Data that Edebug saves and restores. | |
1.13 Macro Calls | Specifying how to handle macro calls. | |
1.14 Edebug Options | Option variables for customizing Edebug. |
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To debug a Emacs Lisp program with Edebug, you must first instrument the Lisp functions that you want to debug. See section Instrumenting for Edebug.
Once a function is instrumented, any call to the function activates
Edebug. Activating Edebug may stop execution and let you step through
the function, or it may update the display and continue execution while
checking for debugging commands, depending on the selected Edebug
execution mode. The initial execution mode is step
, by default,
which does stop execution. See section Edebug Execution Modes.
Within Edebug, you normally view an Emacs buffer showing the source of the Lisp function you are debugging. We call this the Edebug buffer—but note that it is not always the same buffer, and it is not reserved for Edebug use.
An arrow at the left margin indicates the line where the function is executing. Point initially shows where within the line the function is executing, but this ceases to be true if you move point yourself.
If you instrument the definition of fac
(shown below) for Edebug and
then execute (fac 3)
, here is what you normally see. Point is at
the open-parenthesis before if
.
(defun fac (n) =>∗(if (< 0 n) (* n (fac (1- n))) 1))
The places within a function where Edebug can stop execution are called
stop points. These occur both before and after each subexpression
that is a list, and also after each variable reference.
Here we show with periods the stop points found in the function
fac
:
(defun fac (n) .(if .(< 0 n.). .(* n. .(fac (1- n.).).). 1).)
While a buffer is the Edebug buffer, the special commands of Edebug are available in it, instead of many usual editing commands. Type ? to display a list of Edebug commands. In particular, you can exit just the innermost Edebug activation level with C-], and you can return all the way to top level with q.
For example, you can type the Edebug command <SPC> to execute until
the next stop point. If you type <SPC> once after entry to
fac
, here is the state that you get:
(defun fac (n) =>(if ∗(< 0 n) (* n (fac (1- n))) 1))
When Edebug stops execution after an expression, it displays the expression’s value in the echo area. Use the r command to display the value again later.
If no instrumented code is currently being executed, debug
is run
normally. But while Edebug is active, it catches all errors (if
debug-on-error
is non-nil
) and quits (if
debug-on-quit
is non-nil
). When this happens, Edebug
displays the last stop point that it knows about. This may be the
location of a call to a function which was not instrumented, within
which the error actually occurred. Note that you can also get a full
backtrace inside of Edebug (see Miscellaneous).
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In order to use Edebug to debug Lisp code, you must first
instrument the code. Instrumenting a form inserts additional code
into it which invokes Edebug at the proper places. When instrumenting
any kind of definition (not just defun
or defmacro
), only
the executable expressions inside of the definition are instrumented.
If any syntax error is found while instrumenting, point is left at the
error and an invalid-read-syntax
error is signaled.
Edebug knows how to instrument all the standard special forms, interactive forms with or without expression arguments, anonymous lambda expressions, and other defining forms. It cannot know what a user-defined macro will do with the arguments of a macro call so you must tell it; see section Macro Calls for the details.
Once you have loaded Edebug, the command C-M-x
(eval-defun
) is redefined so that when used with a prefix
argument on a definition, it instruments the definition. If the
variable edebug-all-defs
is non-nil
, that inverts the
meaning of the prefix argument: then C-M-x instruments the
definition unless it has a prefix argument. The default value of
edebug-all-defs
is nil
. The command M-x
edebug-all-defs toggles the value of the variable
edebug-all-defs
.
If edebug-all-defs
is non-nil
, then the commands
eval-region
and eval-current-buffer
also instrument any
definitions they evaluate. Similarly, edebug-all-forms
controls
whether eval-region
should instrument any form, even
non-defining forms. The command M-x edebug-all-forms toggles this
option.
Another command, M-x edebug-eval-top-level-form, is available to
instrument any top-level form regardless of the value of
edebug-all-defs
. Additionally, this command will instrument
top-level forms that are not definitions.
Loading a file does not instrument expressions for Edebug.
Evaluations in the minibuffer via eval-expression
(M-ESC)
are never instrumented.
To remove instrumentation from a definition, simply reevaluate it with one of the non-instrumenting commands that evaluate definitions, or reload the file.
See Evaluation for discussion of other evaluation functions available inside of Edebug.
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Edebug supports several execution modes for running the program you are debugging. We call these alternatives Edebug execution modes; do not confuse them with major modes or minor modes. The current Edebug execution 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.
Normally, you specify the Edebug execution mode by typing a command to continue the program in a certain mode. Here is a table of these commands. All except for S resume execution of the program, at least for a certain distance.
Stop: don’t execute any more of the program for now, just wait for more
Edebug commands. (edebug-stop
)
Step: stop at the next stop point encountered. (edebug-step-mode
)
Next: stop at the next stop point encountered after an expression. Also
see edebug-forward-sexp
in Miscellaneous.
(edebug-next-mode
)
Trace: pause one second at each Edebug stop point. (edebug-trace-mode
)
Rapid trace: update at each stop point, but don’t actually
pause. (edebug-Trace-fast-mode
)
Go: run until the next breakpoint. See section Breakpoints. (edebug-go-mode
)
Continue: pause for one second at each breakpoint, but don’t stop. (edebug-continue-mode
)
Rapid continue: update at each breakpoint, but don’t actually pause. (edebug-Continue-fast-mode
)
Go non-stop: ignore breakpoints. You can still stop the program by typing
S. (edebug-Go-nonstop-mode
)
In general, the execution modes earlier in the above list run the program more slowly or stop sooner.
When you enter a new Edebug level, the mode comes from the value of the
variable edebug-initial-mode
. By default, this specifies
step mode. If the mode thus specified does not stop, then the
Edebug level executes the program (or part of it).
While executing or tracing, you can interrupt the execution by typing any Edebug command. Edebug stops the program at the next stop point and then executes the command that you typed. For example, typing t during execution switches to trace mode at the next stop point.
You can use the S command to stop execution without doing anything else.
If your function happens to read input, a character you hit intending to interrupt execution may be read by the function instead. You can avoid such unintended results by paying attention to when your program wants input.
Keyboard macros containing the commands in this section do not completely work: exiting from Edebug, to resume the program, loses track of the keyboard macro. This is not easy to fix.
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Commands described here let you jump to a specified location.
All, except i, use temporary breakpoints to establish the stop
point and then switch to go
mode. Any other breakpoint reached
before the intended stop point will also stop execution. See
Breakpoints for the details on breakpoints.
Run the program forward over one expression. More precisely, set a
temporary breakpoint at the position that C-M-f would reach,
then execute in go
mode so that the program will stop at breakpoints.
With a prefix argument n, the temporary breakpoint is placed n sexps beyond point. If the containing list ends before n more elements, then the place to stop is after the containing expression.
Be careful that the position C-M-f finds is a place that the
program will really get to; this may not be true in a
condition-case
, for example.
This command does forward-sexp
starting at point rather than the
stop point, thus providing more flexibility. If you want to execute one
expression from the current stop point, type w first, to move
point there.
(edebug-forward-sexp
)
Continue “out of” an expression. It places a temporary breakpoint at the end of the sexp containing point. If the containing sexp is the definition itself, it continues until just before the returns. If that is where you are now, it returns from the function and then stops.
In other words, this command does not exit the currently executing definition unless you are positioned after the last sexp.
(edebug-step-out
)
Step into the definition of the function or macro about to be called,
whether or not it has been instrumented. If its location is not known
to Edebug, this command cannot be used. After loading Edebug,
eval-region
records the position of every definition it
evaluates, even if not instrumented.
Use this command when stopped before the call, since otherwise it is too late.
This command does not switch to go
mode; instead you must execute
the arguments before stepping into the function manually. (A future
version will probably do as expected: set a temporary breakpoint on the
first expression in the function and switch to go
mode.)
Although the automatic instrumentation is convenient, one undesirable
side effect of using edebug-step-in
is that it doesn’t later
uninstrument the stepped-into function.
Proceed to the stop point near where point is using a temporary breakpoint.
(edebug-goto-here
)
All the commands in this section may fail to work as expected in case of nonlocal exit, because a nonlocal exit can bypass the temporary breakpoint where you expected the program to stop.
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Some miscellaneous commands are described here.
Display the help message for Edebug.
(edebug-help
)
Abort one level back to the previous command level.
(abort-recursive-edit
)
Return to the top level editor command loop. This exits all recursive
editing levels, including all levels of Edebug activity. However,
instrumented code protected with unwind-protect
or
condition-case
forms may resume debugging.
(top-level
)
Like q but don’t stop even for protected code.
(top-level-nonstop
)
Redisplay the most recently known expression result in the echo area.
(edebug-previous-result
)
Display a backtrace, excluding Edebug’s own functions for clarity.
You cannot use debugger commands in the backtrace buffer in Edebug as you would in the standard debugger.
The backtrace buffer is killed automatically when you continue execution.
From the Edebug recursive edit, you may invoke commands that activate Edebug again recursively. Any time Edebug is active, you can quit to the top level with q or abort one recursive edit level with C-]. You can display a backtrace of all the currently active function and macro calls with d.
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Three more ways to stop execution once it has started are: breakpoints, the global break condition, and persistent breakpoints.
While using Edebug, you can specify breakpoints in the program you are testing: points where execution should stop. You can set a breakpoint at any stop point, as defined in Using Edebug. For setting and unsetting breakpoints, the stop point that is affected is the first one at or after point in the Edebug buffer. Here are the Edebug commands for breakpoints:
Set a breakpoint at the stop point at or after point. If you use a
prefix argument, the breakpoint is temporary (it turns off the first
time it stops the program). (edebug-set-breakpoint
)
Unset the breakpoint (if any) at the stop point at or after the current
point. (edebug-unset-breakpoint
)
Set a conditional breakpoint which stops the program only if condition
evaluates to a non-nil
value. If you use a prefix argument, the
breakpoint is temporary (it turns off the first time it stops the
program). (edebug-set-conditional-breakpoint
)
Move point to the next breakpoint in the current definition.
(edebug-next-breakpoint
)
While in Edebug, you can set a breakpoint with b and unset one with u. First you must 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.
Reinstrumenting a definition clears all its breakpoints.
A conditional breakpoint tests a condition each time the program gets there, to decide whether to stop. To set a conditional breakpoint, use x, and specify the condition expression in the minibuffer. Setting a conditional breakpoint again will put the previously entered expression in the minibuffer.
You can make both conditional and unconditional breakpoints temporary by using a prefix arg to the command to set the breakpoint. After breaking at a temporary breakpoint, it is automatically cleared.
Edebug always stops or pauses at a breakpoint except when the Edebug mode is Go-nonstop. In that mode, it ignores breakpoints entirely.
To find out where your breakpoints are, use the B command, which moves point to the next breakpoint in the definition following point, or to the first breakpoint if there are no following breakpoints. This command does not continue execution—it just moves point in the buffer.
1.6.1 Global Break Condition | Breaking on an event. | |
1.6.2 Persistent Breakpoints | Embedding breakpoints in code. |
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In contrast to breaking when execution reaches specified locations,
you can also cause a break when a certain event occurs. The global
break condition is a condition that is repeatedly evaluated at every
stop point. If it evaluates to a non-nil
value, then execution
is stopped or paused depending on the execution mode, just like a
breakpoint. Any errors that might occur as a result of evaluating the
condition are ignored, as if the result were nil
.
You can set or edit the condition expression, stored in
edebug-global-break-condition
, using X
(edebug-set-global-break-condition
).
Using the global break condition is perhaps the fastest way
to find where in your code some event occurs, but since it is rather
expensive you should reset the condition to nil
when not in use.
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Since all breakpoints in a definition are cleared each time you
reinstrument it, you might rather install a persistent breakpoint
which is simply a call to the function edebug
. You can, of
course, make such a call conditional. For example, in the fac
function, insert the first line as shown below to stop when the argument
reaches zero:
(defun fac (n) (if (= n 0) (edebug)) (if (< 0 n) (* n (fac (1- n))) 1))
When the fac
definition is instrumented and the function is called,
edebug will cause a break before the call to edebug
. Depending on
the execution mode, edebug will stop or pause.
However, if no instrumented code is being executed, calling
edebug
will instead invoke debug
.
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These Edebug commands let you view aspects of the buffer and window status that obtained before entry to Edebug.
View the outside window configuration. (edebug-view-outside
)
Temporarily display the outside current buffer with point at its outside
position. If prefix arg is supplied, sit for
that many seconds instead. (edebug-bounce-point
)
Switch back to the buffer showing the currently executing function, and
move point back to the current stop point. (edebug-where
)
Toggle the edebug-save-windows
variable which indicates whether
the outside window configuration is saved and restored. Also, each time
it is toggled on, make the outside window configuration the same as
the current window configuration.
(edebug-toggle-save-windows
)
You can view the outside window configuration with v or just bounce to the current point in the current buffer with p, even if it is not normally displayed. After moving point, you may wish to pop back to the stop point with w from the Edebug buffer.
By using the W command twice, Edebug again saves and restores the outside window configuration, but to the current configuration. This is a convenient way to, for example, add another buffer to be displayed whenever Edebug is active. However, the automatic redisplay of ‘*edebug*’ and ‘*edebug-trace*’ may conflict with the buffers you wish to see unless you have enough windows open.
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While within Edebug, you can evaluate expressions “as if” Edebug were not running. Edebug tries to be invisible to the expression’s evaluation and printing. See The Outside Context for details on this process. Also see Printing for how to control printing.
Evaluate expression exp in the context outside of Edebug.
That is, Edebug tries to avoid altering the effect of exp.
(edebug-eval-expression
)
Evaluate expression exp in the context of Edebug itself.
Evaluate the expression before point, in the context outside of Edebug.
(edebug-eval-last-sexp
)
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You can use the evaluation list buffer, called ‘*edebug*’, to evaluate expressions interactively. You can also set up the evaluation list of expressions to be evaluated automatically each time Edebug updates the display.
Switch to the evaluation list buffer ‘*edebug*’.
(edebug-visit-eval-list
)
In the ‘*edebug*’ buffer you can use the commands of Lisp Interaction as well as these special commands:
Evaluate the expression before point, in the context outside of Edebug,
and insert the value in the buffer.
(edebug-eval-print-last-sexp
)
Evaluate the expression before point, in the context outside of Edebug.
(edebug-eval-last-sexp
)
Build a new evaluation list from the first expression of each group,
reevaluate and redisplay. Groups are separated by comment lines.
(edebug-update-eval-list
)
Delete the evaluation list group that point is in.
(edebug-delete-eval-item
)
Switch back to the Edebug buffer at the current stop point.
(edebug-where
)
You can evaluate expressions in the evaluation list window with LFD or C-x C-e, just as you would in ‘*scratch*’; but they are evaluated in the context outside of Edebug.
The expressions you enter interactively (and their results) are lost when you continue execution unless you add them to the evaluation list with C-c C-u. This command builds a new list from the first expression of each evaluation list group. Groups are separated by comment lines. Be careful not to add expressions that execute instrumented code otherwise an infinite loop will result.
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 variables not currently valid, for example, do 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*> ;--------------------------------------------------------------- (selected-window) #<window 16 on *scratch*> ;--------------------------------------------------------------- (point) 196 ;--------------------------------------------------------------- bad-var "Symbol's value as variable is void: bad-var" ;--------------------------------------------------------------- (recursion-depth) 0 ;--------------------------------------------------------------- this-command eval-last-sexp ;---------------------------------------------------------------
To delete a group, move point into it and type C-c C-d, or simply delete the text for the group and update the evaluation list with C-c C-u. When you add a new group, be sure it is separated from its neighbors by a comment line.
After selecting ‘*edebug*’, you can return to the source code
buffer (the Edebug buffer) with C-c C-w. The *edebug*
buffer is killed when you continue execution, and
recreated next time it is needed.
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If some structures that may be printed contain circular references to other parts of the same structure, you can print them more usefully with the ‘cust-print’ package.
To load the package and activate custom printing only for Edebug, simply
use the command edebug-install-custom-print-funcs
.
To restore the standard print functions, use
edebug-uninstall-custom-print-funcs
.
While printing results, edebug binds print-length
,
print-level
, and print-circle
to
edebug-print-length
(50
), edebug-print-level
(50
), and edebug-print-circle
(t
) respectively, if
these values are non-nil
.
Here is an example of circular structure printing. An error will still
be generated when format
executes.
(progn (edebug-install-custom-print-funcs) (setq a '(1 2)) (format "%s" (setcar a a)))
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Edebug provides a rudimentary coverage tester and frequency of execution
display. Frequency counts are always accumulated, both before and after
evaluation of each instrumented expression, even if the execution mode
is Go-nonstop. Coverage testing is only done if the option
edebug-test-coverage
is non-nil
because this is relatively
expensive. Both data sets are displayed by
edebug-display-freq-count
.
Display the frequency count data for each line of the current
definition. The frequency counts are inserted as comment lines after
each line, and you can undo all insertions with one undo
command.
The counts are inserted starting under the ( before an expression
or the ) after an expression, or on the last char of a symbol.
The counts are only displayed when they differ from previous counts on
the same line.
If coverage is being tested, whenever all known results of an expression
are eq
, the char = will be appended after the count
for that expression. Note that this is always the case for an
expression only evaluated once.
To clear the frequency count and coverage data for a definition, reinstrument it.
For example, after evaluating (fac 5)
with a persistent
breakpoint, and setting edebug-test-coverage
to t
, the
frequency data is looks like this:
(defun fac (n) (if (= n 0) (edebug)) ;#6 1 0 =5 (if (< 0 n) ;#5 = (* n (fac (1- n))) ;# 5 0 1)) ;# 0
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Edebug tries to be transparent to the program you are debugging. In addition, most evaluations you do within Edebug (see Evaluation) occur in the same outside context which is temporarily restored for the evaluation. But Edebug is not completely successful and this section explains precisely how it fails.
1.12.1 Just Checking | When Edebug decides what to do. | |
1.12.2 Outside Window Configuration | When Edebug updates the display. | |
1.12.3 Edebug Recursive Edit | When Edebug stops execution. | |
1.12.4 Side Effects | How Edebug fails to be transparent. |
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Whenever Edebug is entered just to think about whether to take some action, it needs to save and restore certain data.
max-lisp-eval-depth
and max-specpdl-size
are both
incremented so that your code should not be impacted by Edebug frames on
the stack.
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When Edebug needs to display something (e.g., in trace mode), it saves the current window configuration from “outside” Edebug. When you exit Edebug (by continuing the program), it restores the previous window configuration.
XEmacs redisplays only when it pauses. Usually, when you continue execution, the program comes back into Edebug at a breakpoint or after stepping, without pausing or reading input in between. In such cases, XEmacs never gets a chance to redisplay the “outside” configuration. What you see is the window configuration for within Edebug, with no interruption.
Entry to Edebug for displaying something also saves and restores the following data. (Some of these variables are deliberately not restored if an error or quit signal occurs.)
edebug-save-windows
is non-nil
. It is 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.
edebug-save-displayed-buffer-points
is non-nil
.
overlay-arrow-position
and
overlay-arrow-string
are saved and restored. This permits
recursive use of Edebug, and use of Edebug while using GUD.
cursor-in-echo-area
is locally bound to nil
so that
the cursor shows up in the window.
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When Edebug is entered and actually reads commands from the user, it saves (and later restores) these additional data:
last-command
, this-command
, last-command-char
, and
last-input-char
. Commands used within Edebug do not affect these
variables outside of Edebug.
But note that it is not possible to preserve the status reported by
(this-command-keys)
and the variables unread-command-char
and unread-command-event
.
standard-output
and standard-input
.
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Edebug operation unavoidably alters some data in XEmacs, and this can interfere with debugging certain programs.
max-lisp-eval-depth
and max-specpdl-size
, are also
increased proportionally.
this-command-keys
is changed by
executing commands within Edebug and there is no way to reset
the key sequence from Lisp.
unread-command-char
or unread-command-event
. Entering Edebug while these variables
have nontrivial values can interfere with execution of the program you
are debugging.
command-history
. In rare cases this can alter execution.
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When Edebug instruments an expression that calls a Lisp macro, it needs
additional advice to do the job properly. This is because there is no
way to tell which subexpressions of the macro call may be evaluated.
(Evaluation may occur explicitly in the macro body, or when the
resulting expansion is evaluated, or any time later.) You must explain
the format of macro call arguments by using def-edebug-spec
to
define an Edebug specification for each macro.
Specify which parts of a call to macro macro are subexpressions to be evaluated. The second argument, specification, often looks like the formal macro argument list, but it specifies the structure of the macro call arguments.
The macro argument may be any symbol, not just a macro name, as explained below.
Here is a table of the possibilities for specification and how each directs processing of arguments.
t
All arguments are instrumented for evaluation.
0
None of the arguments is instrumented.
The symbol must have an Edebug specification which is used instead. This indirection is repeated until another kind of specification is found. This allows you to inherit the specification for another macro.
The elements of the list describe the types of the arguments of a calling form. The possible elements of a specification list are described below.
1.13.1 Specification List | How to specify complex patterns of evaluation. | |
1.13.2 Backtracking | What Edebug does when matching fails. | |
1.13.3 Specification Examples |
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A specification list is required if some arguments of a macro call
are evaluated while others are not. Some specification elements in a
specification list match one or more arguments, but others modify the
processing of all following specification elements. The latter, called
special specifications, are symbols beginning with ‘&
’
(e.g. &optional
).
A specification list may contain sublists which match arguments that are themselves lists, or it may contain vectors used for grouping. Sublists and groups thus subdivide the specification list into a hierarchy of levels. Special specifications only apply to the remainder of the sublist or group they are contained in. There is an implicit grouping around each special specification and all following elements in the sublist or group.
If a specification list fails at some level, then backtracking may be invoked to find some alternative at a higher level, or if no alternatives remain, an error will be signaled. See Backtracking for more details.
Edebug specifications provide at least the power of regular expression matching. Additionally, some context free (i.e. finite state with stack) constructs are supported: the matching of sublists with balanced parentheses, recursive processing of forms, and indirect specifications.
Each element of a specification list may be one of the following, with the corresponding type of argument:
sexp
A single unevaluated expression.
form
A single evaluated expression, which is instrumented.
place
A place as in the Common Lisp setf
place argument. It will be
instrumented just like a form, but the macro is expected to strip the
instrumentation using edebug-unwrap
or edebug-unwrap*
.
body
Short for &rest form
. See &rest
below.
function-form
A function form: a quoted function symbol, a quoted lambda expression,
or a form (that should evaluate to a function symbol or lambda
expression). This is useful when function arguments might be quoted
with quote
rather than function
since the body of a lambda
expression will be instrumented either way. See the apply
example
below.
lambda-expr
An unquoted anonymous lambda expression.
&optional
All following elements in the specification list are optional; as soon
as one does not match, Edebug stops matching at this level. To make
just one item optional, use [&optional spec]
. See the
defun
example below.
&rest
All following elements in the specification list are repeated zero or more times. All the elements need not be used in the last repetition, however.
To specify repetition of certain types of arguments, followed by
dissimilar arguments, use [&rest specs…]
.
To specify all elements must match on the last repetition, use
&rest [specs…]
.
&or
Each of the following elements in the specification list is an
alternative, processed left to right until one matches. One of the
alternatives must match otherwise the &or
specification
fails. To group two or more list elements as a single alternative,
enclose them in […]
.
¬
Each of the following elements is matched as alternatives, and if any of
them match, the specification fails. If none of them match, nothing is
matched, but the ¬
specification succeeds. See the
lambda-list
example below.
&define
Indicates that the specification is for a defining form. The defining
form itself is not instrumented, but forms inside it may be. The
&define
keyword must appear first in a top-level list
specification.
Other specifications that may only appear after &define
are
described here. See the defun
example below.
name
The argument, a symbol, is the name of the defining form. But a defining form need not be named at all in which case a unique name will be created for it.
The name
specification may be used more than once in the
specification and each subsequent use will append the corresponding
symbol argument to the previous name with ‘@
’ between them.
This is useful for generating unique but meaningful names for
definitions such as defadvice
and defmethod
.
:name
The specification following :name
is used as an additional name
component for the definition. This is useful to add a unique component
to the definition name. It may be used more than once, and it does not
affect matching of arguments.
arg
The argument, a symbol, is the name of an argument of the defining form.
However, lambda list keywords (symbols starting with ‘&
’)
are not allowed. See lambda-list
and the example below.
lambda-list
This matches the whole argument list of an Emacs Lisp lambda
expression, which is a list of symbols and the keywords
&optional
and &rest
def-body
The argument is the body of code in a definition. This is like
body
, described above, but a definition body must be instrumented
with a special Edebug call. Use def-body
for the highest level
list of forms within the definition.
def-form
The argument is a single top-level form in a definition. This is like
def-body
, except use this to match a single form rather than
a list of forms. As a special case, def-form
also means
that tracing information is not output when the form is executed.
See the interactive
example below.
nil
This is successful when there are no more arguments to match; otherwise
it fails. See sublist specifications and the backquote
example below.
fence
No argument is matched but backtracking through the fence is disabled
while matching the remainder of the specifications at this level. See
Backtracking for more details. Also see the let
example
below.
other-symbol
Any other symbol in a specification list may be a predicate or an indirect specification.
If the symbol has an Edebug specification, this indirect
specification should be a list that is used in-line. The specification
may be defined with def-edebug-spec
just as for macros. See the
defun
example below.
Otherwise, the symbol should be a predicate. The predicate is called with the argument and the specification fails if the predicate fails. The argument is not instrumented.
Predicates that may be used include: symbolp
, integerp
,
stringp
, vectorp
, atom
(which matches a number,
string, symbol, or vector), keywordp
, and
lambda-list-keywordp
. The last two, defined in ‘edebug.el’,
test whether the argument is a symbol starting with ‘:
’ and
‘&
’ respectively.
[elements…]
Rather than matching a vector argument, a vector treats the elements as a single group specification.
"string"
A symbol named string.
'symbol or (quote symbol)
The precise symbol symbol, treated as unevaluated. Use a string instead.
(vector elements…)
A vector whose elements must match the elements in
the specification. See the backquote
example below.
(elements…)
Any other list is a sublist specification and the argument must be a list whose elements match the specification elements.
A sublist specification may be a dotted list and the corresponding list
argument may then be a dotted list. Alternatively, the last cdr of a
dotted list specification may be another sublist specification
(via a grouping or an indirect specification) whose elements match the
non-dotted list arguments. This is useful in recursive specifications
such as in the backquote
example below. Also see the description
of a nil
specification above for terminating such recursion.
Note that a sublist specification that is printed like (specs .
nil)
means the same as (specs)
, and (specs .
(sublist-elements…))
means the same as (specs
sublist-elements…)
.
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If a specification fails to match at some point, this does not necessarily mean a syntax error will be signaled; instead, backtracking will take place until all alternatives have been exhausted. Eventually every element of the argument list must be matched by some element in the specification, and every required element in the specification must match some argument.
The special specifications &optional
, &rest
, or &or
establish alternatives.
Backtracking is disabled for the remainder of a sublist or group when certain conditions occur, described below, and is reenabled when another alternative is established. You might want to disable backtracking to commit to some alternative so that Edebug can provide more specific syntax error messages. Normally, if no alternative matches, Edebug reports that none matched, but if one alternative is committed to, Edebug can report how it failed to match.
First, backtracking is disabled while matching any of the form
specifications (i.e. form
, body
, def-form
, and
def-body
). These specifications will match any form so any error
must be in the form itself rather than at a higher level.
Second, backtracking is disabled after successfully matching a quoted
symbol or string specification. If you have a set of alternative
constructs that all begin with the same symbol, you can usually work
around this limitation by factoring the symbol out of the alternatives,
e.g., ["foo" &or [first case] [second case] ...]
.
Third, backtracking may be explicitly disabled by using the
fence
specification. This is useful when you know that there
can be no higher alternatives.
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This section provides several examples of Edebug specifications to show most of its capabilities.
A let
special form has a sequence of bindings and a body where
each of the bindings is a symbol or a sublist with a symbol and optional
value. In the specification below notice the fence
inside of the
sublist to prevent backtracking.
(def-edebug-spec let ((&rest &or symbolp (fence symbolp &optional form)) body))
Here are the specifications for the case
and do
macros in
‘cl.el’. (Specifications for all the macros defined by
‘cl.el’ (version 2.02) are in ‘cl-specs.el’.)
(def-edebug-spec case (form &rest (sexp body))) (def-edebug-spec do ((&rest &or symbolp (symbolp &optional form form)) (form body) body))
Edebug uses the following specifications for defun
and
defmacro
and the associated argument list and interactive
specifications. It is necessary to specially process the argument of an
interactive form to allow debugging of a list argument outside of the
function body, while not stopping on the interactive form itself.
(def-edebug-spec defmacro defun) ; Indirect ref todefun
spec (def-edebug-spec defun (&define name lambda-list [&optional stringp] ; Match the doc string, if present. [&optional ("interactive" interactive)] def-body)) (def-edebug-spec lambda-list (([&rest arg] [&optional ["&optional" arg &rest arg]] &optional ["&rest" arg] ))) (def-edebug-spec interactive (&optional &or stringp def-form)) ; Notice:def-form
The backquote
specification illustrates how to use nil
to
terminate recursion. Also a vector may be matched.
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.
However, ,
and ,@
forms within backquoted forms are
evaluated and Edebug instruments them.
Nested backquotes are supported to a limited extent. Quoted forms are
not normally evaluated, but if the quoted form appears immediately
within ,
and ,@
forms, Edebug treats this as a backquoted
form at the next higher level.
(def-edebug-spec ` (backquote-form)) (def-edebug-spec backquote-form (&or ([&or "," ",@"] &or ("quote" backquote-form) form) (backquote-form . [&or nil backquote-form]) (vector &rest backquote-form) sexp))
Finally, the standard functions mapcar
, mapconcat
,
mapatoms
, apply
, and funcall
all take function
arguments. Here is one example:
(def-edebug-spec apply (function-form &rest form))
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These options affect the behavior of Edebug:
Functions to call before Edebug is used. Each time it is set to a new
function, Edebug will call that function once and then
edebug-setup-hook
is reset to nil
. You could use this to
load up Edebug specifications associated with a package you are using
only when you also use Edebug.
If non-nil
, normal evaluation of any defining forms (e.g.
defun
and defmacro
) will instrument them for Edebug. This
applies to eval-defun
, eval-region
, and
eval-current-buffer
.
Use the command edebug-all-defs
to toggle the value of
this variable. You may want to make this variable local to each
buffer by calling (make-local-variable 'edebug-all-defs)
in your
emacs-lisp-mode-hook
.
The default value is nil
.
If non-nil
, normal evaluation of any forms by eval-defun
,
eval-region
, and eval-current-buffer
will instrument them
for Edebug.
Use the command edebug-all-forms
to toggle the value of this
option.
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
.
If non-nil
, save and restore point in all displayed buffers.
This 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.
This is an expensive operation since it visits each window and each displayed buffer twice for each Edebug activation, so it is best to avoid it if you can.
If this variable is non-nil
, it specifies the initial execution
mode for Edebug when it is first activated. Possible values are
step
, next
, go
, Go-nonstop
, trace
,
Trace-fast
, continue
, and Continue-fast
.
The default value is step
.
Non-nil
means display 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 this display by replacing functions
edebug-print-trace-before
and edebug-print-trace-after
.
The default value is nil
.
If non-nil
, Edebug tests coverage of all expressions debugged.
This is done by comparing the result of each expression
with the previous result. Coverage is considered OK if two different
results are found. So to sufficiently test the coverage of your code,
try to execute it under conditions that evaluate all expressions more
than once, and produce different results for each expression.
Use edebug-display-freq-count
to display the frequency count and
coverage information for a definition.
If non-nil
, continue defining or executing any keyboard macro
that is executing outside of Edebug.
If non-nil
, set print-length
to this while printing results in
Edebug. The default value is 50
.
If non-nil
, set print-level
to this while printing results in
Edebug. The default value is 50
.
If non-nil
, set print-circle
to this while printing results in
Edebug. The default value is nil
.
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