SGI Freeware 1999 August

home *** CD-ROM | disk | FTP | other *** search

/ SGI Freeware 1999 August / SGI Freeware 1999 August.iso / dist / fw_xemacs.idb / usr / freeware / lib / xemacs-20.4 / info / lispref.info-13.z / lispref.info-13

Wrap

GNU Info File | 1998-05-21 | 50.9 KB | 1,243 lines

This is Info file ../../info/lispref.info, produced by Makeinfo version 1.68 from the input file lispref.texi. Edition History: GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994 XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995 GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp Programmer's Manual (for 19.13) Third Edition, July 1995 XEmacs Lisp Reference Manual (for 19.14 and 20.0) v3.1, March 1996 XEmacs Lisp Reference Manual (for 19.15 and 20.1, 20.2) v3.2, April, May 1997 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc. Copyright (C) 1995, 1996 Ben Wing. 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. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and 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 the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English. File: lispref.info, Node: Using Edebug, Next: Instrumenting, Up: Edebug Using Edebug ------------ To debug an XEmacs Lisp program with Edebug, you must first "instrument" the Lisp code that you want to debug. If you want to just try it now, load `edebug.el', move point into a definition and do `C-u C-M-x' (`eval-defun' with a prefix argument). See *Note Instrumenting:: for alternative ways to instrument code. 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. *Note Edebug Execution Modes::. Within Edebug, you normally view an XEmacs buffer showing the source of the Lisp function you are debugging. This is referred to as the "source code buffer"--but note that it is not always the same buffer depending on which function is currently being executed. 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 you can move point yourself. If you instrument the definition of `fac' (shown below) 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 the source code buffer is selected, the special commands of Edebug are available in it, in addition to the commands of XEmacs Lisp mode. (The buffer is temporarily made read-only, however.) 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 display you will see: (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. Other frequently used commands are `b' to set a breakpoint at a stop point, `g' to execute until a breakpoint is reached, and `q' to exit to the top-level command loop. Type `?' to display a list of all Edebug commands. File: lispref.info, Node: Instrumenting, Next: Edebug Execution Modes, Prev: Using Edebug, Up: Edebug Instrumenting for Edebug ------------------------ 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. Furthermore, if Edebug detects a syntax error while instrumenting, point is left at the erroneous code and an `invalid-read-syntax' error is signaled. Once you have loaded Edebug, the command `C-M-x' (`eval-defun') is redefined so that when invoked with a prefix argument on a definition, it instruments the definition before evaluating it. (The source code itself is not modified.) 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', `eval-current-buffer', and `eval-buffer' also instrument any definitions they evaluate. Similarly, `edebug-all-forms' controls whether `eval-region' should instrument *any* form, even non-defining forms. This doesn't apply to loading or evaluations in the minibuffer. 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' or `edebug-all-forms'. Just before Edebug instruments any code, it calls any functions in the variable `edebug-setup-hook' and resets its value to `nil'. You could use this to load up Edebug specifications associated with a package you are using but only when you also use Edebug. For example, `my-specs.el' may be loaded automatically when you use `my-package' with Edebug by including the following code in `my-package.el'. (add-hook 'edebug-setup-hook (function (lambda () (require 'my-specs)))) While Edebug is active, the command `I' (`edebug-instrument-callee') instruments the definition of the function or macro called by the list form after point, if is not already instrumented. If the location of the definition 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 instrumenting it. Also see the command `i' (*Note Jumping::) which steps into the callee. Edebug knows how to instrument all the standard special forms, an interactive form with an expression argument, anonymous lambda expressions, and other defining forms. (Specifications for macros defined by `cl.el' (version 2.03) are provided in `cl-specs.el'.) Edebug cannot know what a user-defined macro will do with the arguments of a macro call so you must tell it. See *Note Instrumenting Macro Calls:: for the details. Note that a couple ways remain to evaluate expressions without instrumenting them. Loading a file via the `load' subroutine does not instrument expressions for Edebug. Evaluations in the minibuffer via `eval-expression' (`M-ESC') are not instrumented. To remove instrumentation from a definition, simply reevaluate it with one of the non-instrumenting commands, or reload the file. See *Note Edebug Eval:: for other evaluation functions available inside of Edebug. File: lispref.info, Node: Edebug Execution Modes, Next: Jumping, Prev: Instrumenting, Up: Edebug Edebug Execution Modes ---------------------- 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 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. `S' Stop: don't execute any more of the program for now, just wait for more Edebug commands (`edebug-stop'). `<SPC>' Step: stop at the next stop point encountered (`edebug-step-mode'). `n' Next: stop at the next stop point encountered after an expression (`edebug-next-mode'). Also see `edebug-forward-sexp' in *Note Edebug Misc::. `t' Trace: pause one second at each Edebug stop point (`edebug-trace-mode'). `T' Rapid trace: update at each stop point, but don't actually pause (`edebug-Trace-fast-mode'). `g' Go: run until the next breakpoint (`edebug-go-mode'). *Note Breakpoints::. `c' Continue: pause for one second at each breakpoint, but don't stop (`edebug-continue-mode'). `C' Rapid continue: update at each breakpoint, but don't actually pause (`edebug-Continue-fast-mode'). `G' Go non-stop: ignore breakpoints (`edebug-Go-nonstop-mode'). You can still stop the program by hitting any key. 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 initial execution mode comes from the value of the variable `edebug-initial-mode'. By default, this specifies `step' mode. Note that you may reenter the same Edebug level several times if, for example, an instrumented function is called several times from one command. 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 `S' 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 Edebug commands do not work; when you exit from Edebug, to resume the program, whether you are defining or executing a keyboard macro is forgotten. Also, defining or executing a keyboard macro outside of Edebug does not affect the command loop inside Edebug. This is usually an advantage. But see `edebug-continue-kbd-macro'. File: lispref.info, Node: Jumping, Next: Edebug Misc, Prev: Edebug Execution Modes, Up: Edebug Jumping ------- 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 *Note Breakpoints:: for the details on breakpoints. `f' Run the program forward over one expression (`edebug-forward-sexp'). 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 `cond', for example. This command does `forward-sexp' starting at point rather than the stop point. If you want to execute one expression from the current stop point, type `w' first, to move point there. `o' Continue "out of" an expression (`edebug-step-out'). It places a temporary breakpoint at the end of the sexp containing point. If the containing sexp is a function definition itself, it continues until just before the last sexp in the definition. 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 function unless you are positioned after the last sexp. `I' Step into the function or macro after point after first ensuring that it is instrumented. It does this by calling `edebug-on-entry' and then switching to `go' mode. Although the automatic instrumentating is convenient, it is not later automatically uninstrumented. `h' 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. File: lispref.info, Node: Edebug Misc, Next: Breakpoints, Prev: Jumping, Up: Edebug Miscellaneous ------------- Some miscellaneous commands are described here. `?' Display the help message for Edebug (`edebug-help'). `C-]' Abort one level back to the previous command level (`abort-recursive-edit'). `q' Return to the top level editor command loop (`top-level'). 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. `Q' Like `q' but don't stop even for protected code (`top-level-nonstop'). `r' Redisplay the most recently known expression result in the echo area (`edebug-previous-result'). `d' Display a backtrace, excluding Edebug's own functions for clarity (`edebug-backtrace'). 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 pending evaluations with `d'. File: lispref.info, Node: Breakpoints, Next: Trapping Errors, Prev: Edebug Misc, Up: Edebug Breakpoints ----------- There are three more ways to stop execution once it has started: breakpoints, the global break condition, and embedded 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 *Note Using Edebug::. For setting and unsetting breakpoints, the stop point that is affected is the first one at or after point in the source code buffer. Here are the Edebug commands for breakpoints: `b' Set a breakpoint at the stop point at or after point (`edebug-set-breakpoint'). If you use a prefix argument, the breakpoint is temporary (it turns off the first time it stops the program). `u' Unset the breakpoint (if any) at the stop point at or after the current point (`edebug-unset-breakpoint'). `x CONDITION <RET>' Set a conditional breakpoint which stops the program only if CONDITION evaluates to a non-`nil' value (`edebug-set-conditional-breakpoint'). If you use a prefix argument, the breakpoint is temporary (it turns off the first time it stops the program). `B' Move point to the next breakpoint in the 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. Reevaluating or reinstrumenting a definition clears all its breakpoints. A "conditional breakpoint" tests a condition each time the program gets there. To set a conditional breakpoint, use `x', and specify the condition expression in the minibuffer. Setting a conditional breakpoint at a stop point that already has a conditional breakpoint puts the current condition expression in the minibuffer so you can edit it. 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 `B', 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. * Menu: * Global Break Condition:: Breaking on an event. * Embedded Breakpoints:: Embedding breakpoints in code. File: lispref.info, Node: Global Break Condition, Next: Embedded Breakpoints, Up: Breakpoints Global Break Condition ...................... 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. File: lispref.info, Node: Embedded Breakpoints, Prev: Global Break Condition, Up: Breakpoints Embedded Breakpoints .................... Since all breakpoints in a definition are cleared each time you reinstrument it, you might rather create an "embedded 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 stop 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'. Calling `debug' will always invoke the standard backtrace debugger. File: lispref.info, Node: Trapping Errors, Next: Edebug Views, Prev: Breakpoints, Up: Edebug Trapping Errors --------------- An error may be signaled by subroutines or XEmacs Lisp code. If a signal is not handled by a `condition-case', this indicates an unrecognized situation has occurred. If Edebug is not active when an unhandled error is signaled, `debug' is run normally (if `debug-on-error' is non-`nil'). But while Edebug is active, `debug-on-error' and `debug-on-quit' are bound to `edebug-on-error' and `edebug-on-quit', which are both `t' by default. Actually, if `debug-on-error' already has a non-`nil' value, that value is still used. It is best to change the values of `edebug-on-error' or `edebug-on-quit' when Edebug is not active since their values won't be used until the next time Edebug is invoked at a deeper command level. If you only change `debug-on-error' or `debug-on-quit' while Edebug is active, these changes will be forgotten when Edebug becomes inactive. Furthermore, during Edebug's recursive edit, these variables are bound to the values they had outside of Edebug. Edebug shows you the last stop point that it knew about before the error was signaled. This may be the location of a call to a function which was not instrumented, within which the error actually occurred. For an unbound variable error, the last known stop point might be quite distant from the offending variable. If the cause of the error is not obvious at first, note that you can also get a full backtrace inside of Edebug (see *Note Edebug Misc::). Edebug can also trap signals even if they are handled. If `debug-on-error' is a list of signal names, Edebug will stop when any of these errors are signaled. Edebug shows you the last known stop point just as for unhandled errors. After you continue execution, the error is signaled again (but without being caught by Edebug). Edebug can only trap errors that are handled if they are signaled in Lisp code (not subroutines) since it does so by temporarily replacing the `signal' function. File: lispref.info, Node: Edebug Views, Next: Edebug Eval, Prev: Trapping Errors, Up: Edebug Edebug Views ------------ The following Edebug commands let you view aspects of the buffer and window status that obtained before entry to Edebug. `v' View the outside window configuration (`edebug-view-outside'). `p' Temporarily display the outside current buffer with point at its outside position (`edebug-bounce-point'). If prefix arg is supplied, sit for that many seconds instead. `w' Move point back to the current stop point (`edebug-where') in the source code buffer. Also, if you use this command in another window displaying the same buffer, this window will be used instead to display the buffer in the future. `W' Toggle the `edebug-save-windows' variable which indicates whether the outside window configuration is saved and restored (`edebug-toggle-save-windows'). Also, each time it is toggled on, make the outside window configuration the same as the current window configuration. With a prefix argument, `edebug-toggle-save-windows' only toggles saving and restoring of the selected window. To specify a window that is not displaying the source code buffer, you must use `C-xXW' from the global keymap. 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 a source code buffer. By using `W' 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. File: lispref.info, Node: Edebug Eval, Next: Eval List, Prev: Edebug Views, Up: Edebug Evaluation ---------- 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. Evaluation of expressions that cause side effects will work as expected except for things that Edebug explicitly saves and restores. See *Note The Outside Context:: for details on this process. Also see *Note Reading in Edebug:: and *Note Printing in Edebug:: for topics related to evaluation. `e EXP <RET>' Evaluate expression EXP in the context outside of Edebug (`edebug-eval-expression'). In other words, Edebug tries to avoid altering the effect of EXP. `M-<ESC> EXP <RET>' Evaluate expression EXP in the context of Edebug itself. `C-x C-e' Evaluate the expression before point, in the context outside of Edebug (`edebug-eval-last-sexp'). Edebug supports evaluation of expressions containing references to lexically bound symbols created by the following constructs in `cl.el' (version 2.03 or later): `lexical-let', `macrolet', and `symbol-macrolet'. File: lispref.info, Node: Eval List, Next: Reading in Edebug, Prev: Edebug Eval, Up: Edebug Evaluation List Buffer ---------------------- 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. `E' 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: `LFD' Evaluate the expression before point, in the outside context, and insert the value in the buffer (`edebug-eval-print-last-sexp'). `C-x C-e' Evaluate the expression before point, in the context outside of Edebug (`edebug-eval-last-sexp'). `C-c C-u' Build a new evaluation list from the first expression of each group, reevaluate and redisplay (`edebug-update-eval-list'). Groups are separated by comment lines. `C-c C-d' Delete the evaluation list group that point is in (`edebug-delete-eval-item'). `C-c C-w' Switch back to the source code 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, for example, use variables not currently valid 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 with `C-c C-w'. The `*edebug*' buffer is killed when you continue execution, and recreated next time it is needed. File: lispref.info, Node: Reading in Edebug, Next: Printing in Edebug, Prev: Eval List, Up: Edebug Reading in Edebug ----------------- To instrument a form, Edebug first reads the whole form. Edebug replaces the standard Lisp Reader with its own reader that remembers the positions of expressions. This reader is used by the Edebug replacements for `eval-region', `eval-defun', `eval-buffer', and `eval-current-buffer'. Another package, `cl-read.el', replaces the standard reader with one that understands Common Lisp reader macros. If you use that package, Edebug will automatically load `edebug-cl-read.el' to provide corresponding reader macros that remember positions of expressions. If you define new reader macros, you will have to define similar reader macros for Edebug. File: lispref.info, Node: Printing in Edebug, Next: Tracing, Prev: Reading in Edebug, Up: Edebug Printing in Edebug ------------------ If the result of an expression in your program contains a circular reference, you may get an error when Edebug attempts to print it. You can set `print-length' to a non-zero value to limit the print length of lists (the number of cdrs), and in Emacs 19, set `print-level' to a non-zero value to limit the print depth of lists. But you can print such circular structures and structures that share elements more informatively by using the `cust-print' package. To load `cust-print' and activate custom printing only for Edebug, simply use the command `M-x edebug-install-custom-print'. To restore the standard print functions, use `M-x edebug-uninstall-custom-print'. You can also activate custom printing for printing in any Lisp code; see the package for details. Here is an example of code that creates a circular structure: (progn (edebug-install-custom-print) (setq a '(x y)) (setcar a a)) Edebug will print the result of the `setcar' as `Result: #1=(#1# y)'. The `#1=' notation names the structure that follows it, and the `#1#' notation references the previously named structure. This notation is used for any shared elements of lists or vectors. Independent of whether `cust-print' is active, 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'. Also, `print-readably' is bound to `nil' since some objects simply cannot be printed readably. File: lispref.info, Node: Tracing, Next: Coverage Testing, Prev: Printing in Edebug, Up: Edebug Tracing ------- In addition to automatic stepping through source code, which is also called *tracing* (see *Note Edebug Execution Modes::), Edebug can produce a traditional trace listing of execution in a separate buffer, `*edebug-trace*'. If the variable `edebug-trace' is non-nil, each function entry and exit adds lines to the trace buffer. On function entry, Edebug prints `::::{' followed by the function name and argument values. On function exit, Edebug prints `::::}' followed by the function name and result of the function. The number of `:'s is computed from the recursion depth. The balanced braces in the trace buffer can be used to find the matching beginning or end of function calls. These displays may be customized by replacing the functions `edebug-print-trace-before' and `edebug-print-trace-after', which take an arbitrary message string to print. The macro `edebug-tracing' provides tracing similar to function enter and exit tracing, but for arbitrary expressions. This macro should be explicitly inserted by you around expressions you wish to trace the execution of. The first argument is a message string (evaluated), and the rest are expressions to evaluate. The result of the last expression is returned. Finally, you can insert arbitrary strings into the trace buffer with explicit calls to `edebug-trace'. The arguments of this function are the same as for `message', but a newline is always inserted after each string printed in this way. `edebug-tracing' and `edebug-trace' insert lines in the trace buffer even if Edebug is not active. Every time the trace buffer is added to, the window is scrolled to show the last lines inserted. (There may be some display problems if you use tracing along with the evaluation list.) File: lispref.info, Node: Coverage Testing, Next: The Outside Context, Prev: Tracing, Up: Edebug Coverage Testing ---------------- Edebug provides a rudimentary coverage tester and display of execution frequency. 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 `M-x edebug-display-freq-count'. - Command: 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 an embedded breakpoint, and setting `edebug-test-coverage' to `t', when the breakpoint is reached, 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 The comment lines show that `fac' has been called 6 times. The first `if' statement has returned 5 times with the same result each time, and the same is true for the condition on the second `if'. The recursive call of `fac' has not returned at all. File: lispref.info, Node: The Outside Context, Next: Instrumenting Macro Calls, Prev: Coverage Testing, Up: Edebug The Outside Context ------------------- Edebug tries to be transparent to the program you are debugging. In addition, most evaluations you do within Edebug (see *Note Edebug Eval::) 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. Edebug operation unavoidably alters some data in XEmacs, and this can interfere with debugging certain programs. Also notice that Edebug's protection against change of outside data means that any side effects *intended* by the user in the course of debugging will be defeated. * Menu: * Checking Whether to Stop:: When Edebug decides what to do. * Edebug Display Update:: When Edebug updates the display. * Edebug Recursive Edit:: When Edebug stops execution. File: lispref.info, Node: Checking Whether to Stop, Next: Edebug Display Update, Up: The Outside Context Checking Whether to Stop ........................ 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 one time to reduce Edebug's impact on the stack. You could, however, still run out of stack space when using Edebug. * The state of keyboard macro execution is saved and restored. While Edebug is active, `executing-macro' is bound to `edebug-continue-kbd-macro'. File: lispref.info, Node: Edebug Display Update, Next: Edebug Recursive Edit, Prev: Checking Whether to Stop, Up: The Outside Context Edebug Display Update ..................... 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 same window configuration as the last time Edebug was active, with no interruption. Entry to Edebug for displaying something also saves and restores the following data, but some of these are deliberately not restored if an error or quit signal occurs. * Which buffer is current, and where point and mark are in the current buffer are saved and restored. * The Edebug Display Update, is saved and restored if `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. If the value of `edebug-save-windows' is a list, only the listed windows are saved and restored. The window start and horizontal scrolling of the source code buffer are not restored, however, so that the display remains coherent. * The value of point in each displayed buffer is saved and restored if `edebug-save-displayed-buffer-points' is non-`nil'. * The variables `overlay-arrow-position' and `overlay-arrow-string' are saved and restored. So you can safely invoke Edebug from the recursive edit elsewhere in the same buffer. * `cursor-in-echo-area' is locally bound to `nil' so that the cursor shows up in the window. File: lispref.info, Node: Edebug Recursive Edit, Prev: Edebug Display Update, Up: The Outside Context Edebug Recursive Edit ..................... When Edebug is entered and actually reads commands from the user, it saves (and later restores) these additional data: * The current match data, for whichever buffer was current. * `last-command', `this-command', `last-command-char', `last-input-char', `last-input-event', `last-command-event', `last-event-frame', `last-nonmenu-event', and `track-mouse' . Commands used within Edebug do not affect these variables outside of Edebug. The key sequence returned by `this-command-keys' is changed by executing commands within Edebug and there is no way to reset the key sequence from Lisp. For Emacs 18, Edebug cannot save and restore the value of `unread-command-char'. Entering Edebug while this variable has a nontrivial value can interfere with execution of the program you are debugging. * Complex commands executed while in Edebug are added to the variable `command-history'. In rare cases this can alter execution. * Within Edebug, the recursion depth appears one deeper than the recursion depth outside Edebug. This is not true of the automatically updated evaluation list window. * `standard-output' and `standard-input' are bound to `nil' by the `recursive-edit', but Edebug temporarily restores them during evaluations. * The state of keyboard macro definition is saved and restored. While Edebug is active, `defining-kbd-macro' is bound to `edebug-continue-kbd-macro'. File: lispref.info, Node: Instrumenting Macro Calls, Next: Edebug Options, Prev: The Outside Context, Up: Edebug Instrumenting Macro Calls ------------------------- 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. - Macro: def-edebug-spec MACRO SPECIFICATION Specify which expressions of a call to macro MACRO are forms to be evaluated. For simple macros, the SPECIFICATION often looks very similar to the formal argument list of the macro definition, but specifications are much more general than macro arguments. The MACRO argument may actually be any symbol, not just a macro name. Unless you are using Emacs 19 or XEmacs, this macro is only defined in Edebug, so you may want to use the following which is equivalent: `(put 'MACRO 'edebug-form-spec 'SPECIFICATION)' Here is a simple example that defines the specification for the `for' macro described in the XEmacs Lisp Reference Manual, followed by an alternative, equivalent specification. (def-edebug-spec for (symbolp "from" form "to" form "do" &rest form)) (def-edebug-spec for (symbolp ['from form] ['to form] ['do body])) 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. *a symbol 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. *a list The elements of the list describe the types of the arguments of a calling form. The possible elements of a specification list are described in the following sections. * Menu: * Specification List:: How to specify complex patterns of evaluation. * Backtracking:: What Edebug does when matching fails. * Debugging Backquote:: Debugging Backquote * Specification Examples:: To help understand specifications. File: lispref.info, Node: Specification List, Next: Backtracking, Up: Instrumenting Macro Calls Specification List .................. A "specification list" is required for an Edebug specification if some arguments of a macro call are evaluated while others are not. Some elements in a specification list match one or more arguments, but others modify the processing of all following elements. The latter, called "keyword 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. Keyword specifications only apply to the remainder of the sublist or group they are contained in and there is an implicit grouping around a keyword 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 *Note Backtracking:: for more details. Edebug specifications provide at least the power of regular expression matching. Some context-free constructs are also supported: the matching of sublists with balanced parentheses, recursive processing of forms, and recursion via 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. Two functions, `edebug-unwrap' and `edebug-unwrap*', are provided to strip the instrumentation one level or recursively at all levels. `body' Short for `&rest form'. See `&rest' below. `function-form' A function form: either 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. `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 a few elements optional followed by non-optional elements, use `[&optional SPECS...]'. To specify that several elements should all succeed together, use `&optional [SPECS...]'. See the `defun' example below. `&rest' All following elements in the specification list are repeated zero or more times. All the elements need not match in the last repetition, however. To repeat only a few elements, use `[&rest SPECS...]'. To specify all elements must match on every 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. Each list element following `&or' is a single alternative even if it is a keyword specification. (This breaks the implicit grouping rule.) To group two or more list elements as a single alternative, enclose them in `[...]'. `¬' Each of the following elements is matched as alternatives as if by using `&or', but if any of them match, the specification fails. If none of them match, nothing is matched, but the `¬' specification succeeds. `&define' Indicates that the specification is for a defining form. The defining form itself is not instrumented (i.e. Edebug does not stop before and after the defining form), but forms inside it typically will be instrumented. The `&define' keyword should be the first element in a list specification. Additional 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 element following `:name' should be a symbol; it is used as an additional name component for the definition. This is useful to add a unique, static component to the name of the definition. It may be used more than once. No argument is matched. `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 XEmacs 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 different Edebug call that looks up information associated with the definition. Use `def-body' for the highest level list of forms within the definition. `def-form' The argument is a single, highest-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 at the current argument list level; otherwise it fails. See sublist specifications and the backquote example below. `gate' No argument is matched but backtracking through the gate is disabled while matching the remainder of the specifications at this level. This is primarily used to generate more specific syntax error messages. See *Note 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 either a list specification that is used in place of the symbol, or a function that is called to process the arguments. 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"' The argument should be a symbol named STRING. This specification is equivalent to the quoted symbol, `'SYMBOL', where the name of SYMBOL is the STRING, but the string form is preferred. `'SYMBOL or (quote SYMBOL)' The argument should be the symbol SYMBOL. But use a string specification instead. `(vector ELEMENTS...)' The argument should be 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, e.g. `(spec . [(more specs...)])') 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 of the form `(specs . nil)' means the same as `(specs)', and `(specs . (sublist-elements...))' means the same as `(specs sublist-elements...)'.