This is Info file elisp, produced by Makeinfo-1.55 from the input file elisp.texi. This version is the edition 2.3 of the GNU Emacs Lisp Reference Manual. It corresponds to Emacs Version 19.23. Published by the Free Software Foundation 675 Massachusetts Avenue Cambridge, MA 02139 USA Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. 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: elisp, Node: Using Debugger, Next: Debugger Commands, Prev: Explicit Debug, Up: Debugger Using the Debugger ------------------ When the debugger is entered, it displays the previously selected buffer in one window and a buffer named `*Backtrace*' in another window. The backtrace buffer contains one line for each level of Lisp function execution currently going on. At the beginning of this buffer is a message describing the reason that the debugger was invoked (such as the error message and associated data, if it was invoked due to an error). The backtrace buffer is read-only and uses a special major mode, Debugger mode, in which letters are defined as debugger commands. The usual Emacs editing commands are available; thus, you can switch windows to examine the buffer that was being edited at the time of the error, switch buffers, visit files, or do any other sort of editing. However, the debugger is a recursive editing level (*note Recursive Editing::.) and it is wise to go back to the backtrace buffer and exit the debugger (with the `q' command) when you are finished with it. Exiting the debugger gets out of the recursive edit and kills the backtrace buffer. The backtrace buffer shows you the functions that are executing and their argument values. It also allows you to specify a stack frame by moving point to the line describing that frame. (A stack frame is the place where the Lisp interpreter records information about a particular invocation of a function.) The frame whose line point is on is considered the "current frame". Some of the debugger commands operate on the current frame. The debugger itself must be run byte-compiled, since it makes assumptions about how many stack frames are used for the debugger itself. These assumptions are false if the debugger is running interpreted.  File: elisp, Node: Debugger Commands, Next: Invoking the Debugger, Prev: Using Debugger, Up: Debugger Debugger Commands ----------------- Inside the debugger (in Debugger mode), these special commands are available in addition to the usual cursor motion commands. (Keep in mind that all the usual facilities of Emacs, such as switching windows or buffers, are still available.) The most important use of debugger commands is for stepping through code, so that you can see how control flows. The debugger can step through the control structures of an interpreted function, but cannot do so in a byte-compiled function. If you would like to step through a byte-compiled function, replace it with an interpreted definition of the same function. (To do this, visit the source file for the function and type `C-M-x' on its definition.) Here is a list of Debugger mode commands: `c' Exit the debugger and continue execution. When continuing is possible, it resumes execution of the program as if the debugger had never been entered (aside from the effect of any variables or data structures you may have changed while inside the debugger). Continuing is possible after entry to the debugger due to function entry or exit, explicit invocation, or quitting. You cannot continue if the debugger was entered because of an error. `d' Continue execution, but enter the debugger the next time any Lisp function is called. This allows you to step through the subexpressions of an expression, seeing what values the subexpressions compute, and what else they do. The stack frame made for the function call which enters the debugger in this way will be flagged automatically so that the debugger will be called again when the frame is exited. You can use the `u' command to cancel this flag. `b' Flag the current frame so that the debugger will be entered when the frame is exited. Frames flagged in this way are marked with stars in the backtrace buffer. `u' Don't enter the debugger when the current frame is exited. This cancels a `b' command on that frame. `e' Read a Lisp expression in the minibuffer, evaluate it, and print the value in the echo area. The debugger alters certain important variables as part of its operation; `e' temporarily restores their outside-the-debugger values so you can examine them. This makes the debugger more transparent. By contrast, `M-ESC' does nothing special in the debugger; it shows you the variable values within the debugger. `q' Terminate the program being debugged; return to top-level Emacs command execution. If the debugger was entered due to a `C-g' but you really want to quit, and not debug, use the `q' command. `r' Return a value from the debugger. The value is computed by reading an expression with the minibuffer and evaluating it. The `r' command is useful when the debugger was invoked due to exit from a Lisp call frame (as requested with `b'); then the value specified in the `r' command is used as the value of that frame. It is also useful if you call `debug' and use its return value. Otherwise, `r' has the same effect as `c', and the specified return value does not matter. You can't use `r' when the debugger was entered due to an error.  File: elisp, Node: Invoking the Debugger, Next: Internals of Debugger, Prev: Debugger Commands, Up: Debugger Invoking the Debugger --------------------- Here we describe fully the function used to invoke the debugger. - Function: debug &rest DEBUGGER-ARGS This function enters the debugger. It switches buffers to a buffer named `*Backtrace*' (or `*Backtrace*<2>' if it is the second recursive entry to the debugger, etc.), and fills it with information about the stack of Lisp function calls. It then enters a recursive edit, showing the backtrace buffer in Debugger mode. The Debugger mode `c' and `r' commands exit the recursive edit; then `debug' switches back to the previous buffer and returns to whatever called `debug'. This is the only way the function `debug' can return to its caller. If the first of the DEBUGGER-ARGS passed to `debug' is `nil' (or if it is not one of the special values in the table below), then `debug' displays the rest of its arguments at the the top of the `*Backtrace*' buffer. This mechanism is used to display a message to the user. However, if the first argument passed to `debug' is one of the following special values, then it has special significance. Normally, these values are passed to `debug' only by the internals of Emacs and the debugger, and not by programmers calling `debug'. The special values are: `lambda' A first argument of `lambda' means `debug' was called because of entry to a function when `debug-on-next-call' was non-`nil'. The debugger displays `Entering:' as a line of text at the top of the buffer. `debug' `debug' as first argument indicates a call to `debug' because of entry to a function that was set to debug on entry. The debugger displays `Entering:', just as in the `lambda' case. It also marks the stack frame for that function so that it will invoke the debugger when exited. `t' When the first argument is `t', this indicates a call to `debug' due to evaluation of a list form when `debug-on-next-call' is non-`nil'. The debugger displays the following as the top line in the buffer: Beginning evaluation of function call form: `exit' When the first argument is `exit', it indicates the exit of a stack frame previously marked to invoke the debugger on exit. The second argument given to `debug' in this case is the value being returned from the frame. The debugger displays `Return value:' on the top line of the buffer, followed by the value being returned. `error' When the first argument is `error', the debugger indicates that it is being entered because an error or `quit' was signaled and not handled, by displaying `Signaling:' followed by the error signaled and any arguments to `signal'. For example, (let ((debug-on-error t)) (/ 1 0)) ------ Buffer: *Backtrace* ------ Signaling: (arith-error) /(1 0) ... ------ Buffer: *Backtrace* ------ If an error was signaled, presumably the variable `debug-on-error' is non-`nil'. If `quit' was signaled, then presumably the variable `debug-on-quit' is non-`nil'. `nil' Use `nil' as the first of the DEBUGGER-ARGS when you want to enter the debugger explicitly. The rest of the DEBUGGER-ARGS are printed on the top line of the buffer. You can use this feature to display messages--for example, to remind yourself of the conditions under which `debug' is called.  File: elisp, Node: Internals of Debugger, Prev: Invoking the Debugger, Up: Debugger Internals of the Debugger ------------------------- This section describes functions and variables used internally by the debugger. - Variable: debugger The value of this variable is the function to call to invoke the debugger. Its value must be a function of any number of arguments (or, more typically, the name of a function). Presumably this function will enter some kind of debugger. The default value of the variable is `debug'. The first argument that Lisp hands to the function indicates why it was called. The convention for arguments is detailed in the description of `debug'. - Command: backtrace This function prints a trace of Lisp function calls currently active. This is the function used by `debug' to fill up the `*Backtrace*' buffer. It is written in C, since it must have access to the stack to determine which function calls are active. The return value is always `nil'. In the following example, a Lisp expression calls `backtrace' explicitly. This prints the backtrace to the stream `standard-output': in this case, to the buffer `backtrace-output'. Each line of the backtrace represents one function call. The line shows the values of the function's arguments if they are all known. If they are still being computed, the line says so. The arguments of special forms are elided. (with-output-to-temp-buffer "backtrace-output" (let ((var 1)) (save-excursion (setq var (eval '(progn (1+ var) (list 'testing (backtrace)))))))) => nil ----------- Buffer: backtrace-output ------------ backtrace() (list ...computing arguments...) (progn ...) eval((progn (1+ var) (list (quote testing) (backtrace)))) (setq ...) (save-excursion ...) (let ...) (with-output-to-temp-buffer ...) eval-region(1973 2142 #) byte-code("... for eval-print-last-sexp ...") eval-print-last-sexp(nil) * call-interactively(eval-print-last-sexp) ----------- Buffer: backtrace-output ------------ The character `*' indicates a frame whose debug-on-exit flag is set. - Variable: debug-on-next-call If this variable is non-`nil', it says to call the debugger before the next `eval', `apply' or `funcall'. Entering the debugger sets `debug-on-next-call' to `nil'. The `d' command in the debugger works by setting this variable. - Function: backtrace-debug LEVEL FLAG This function sets the debug-on-exit flag of the stack frame LEVEL levels down the stack, giving it the value FLAG. If FLAG is non-`nil', this will cause the debugger to be entered when that frame later exits. Even a nonlocal exit through that frame will enter the debugger. This function is used only by the debugger. - Variable: command-debug-status This variable records the debugging status of current interactive command. Each time a command is called interactively, this variable is bound to `nil'. The debugger can set this variable to leave information for future debugger invocations during the same command. The advantage, for the debugger, of using this variable rather than another global variable is that the data will never carry over to a subsequent command invocation. - Function: backtrace-frame FRAME-NUMBER The function `backtrace-frame' is intended for use in Lisp debuggers. It returns information about what computation is happening in the stack frame FRAME-NUMBER levels down. If that frame has not evaluated the arguments yet (or is a special form), the value is `(nil FUNCTION ARG-FORMS...)'. If that frame has evaluated its arguments and called its function already, the value is `(t FUNCTION ARG-VALUES...)'. In the return value, FUNCTION is whatever was supplied as the CAR of the evaluated list, or a `lambda' expression in the case of a macro call. If the function has a `&rest' argument, that is represented as the tail of the list ARG-VALUES. If FRAME-NUMBER is out of range, `backtrace-frame' returns `nil'.  File: elisp, Node: Syntax Errors, Next: Compilation Errors, Prev: Debugger, Up: Debugging Debugging Invalid Lisp Syntax ============================= The Lisp reader reports invalid syntax, but cannot say where the real problem is. For example, the error "End of file during parsing" in evaluating an expression indicates an excess of open parentheses (or square brackets). The reader detects this imbalance at the end of the file, but it cannot figure out where the close parenthesis should have been. Likewise, "Invalid read syntax: ")"" indicates an excess close parenthesis or missing open parenthesis, but does not say where the missing parenthesis belongs. How, then, to find what to change? If the problem is not simply an imbalance of parentheses, a useful technique is to try `C-M-e' at the beginning of each defun, and see if it goes to the place where that defun appears to end. If it does not, there is a problem in that defun. However, unmatched parentheses are the most common syntax errors in Lisp, and we can give further advice for those cases. * Menu: * Excess Open:: How to find a spurious open paren or missing close. * Excess Close:: How to find a spurious close paren or missing open.  File: elisp, Node: Excess Open, Next: Excess Close, Up: Syntax Errors Excess Open Parentheses ----------------------- The first step is to find the defun that is unbalanced. If there is an excess open parenthesis, the way to do this is to insert a close parenthesis at the end of the file and type `C-M-b' (`backward-sexp'). This will move you to the beginning of the defun that is unbalanced. (Then type `C-SPC C-_ C-u C-SPC' to set the mark there, undo the insertion of the close parenthesis, and finally return to the mark.) The next step is to determine precisely what is wrong. There is no way to be sure of this except to study the program, but often the existing indentation is a clue to where the parentheses should have been. The easiest way to use this clue is to reindent with `C-M-q' and see what moves. Before you do this, make sure the defun has enough close parentheses. Otherwise, `C-M-q' will get an error, or will reindent all the rest of the file until the end. So move to the end of the defun and insert a close parenthesis there. Don't use `C-M-e' to move there, since that too will fail to work until the defun is balanced. Now you can go to the beginning of the defun and type `C-M-q'. Usually all the lines from a certain point to the end of the function will shift to the right. There is probably a missing close parenthesis, or a superfluous open parenthesis, near that point. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the `C-M-q' with `C-_', since the old indentation is probably appropriate to the intended parentheses. After you think you have fixed the problem, use `C-M-q' again. If the old indentation actually fit the intended nesting of parentheses, and you have put back those parentheses, `C-M-q' should not change anything.  File: elisp, Node: Excess Close, Prev: Excess Open, Up: Syntax Errors Excess Close Parentheses ------------------------ To deal with an excess close parenthesis, first insert an open parenthesis at the beginning of the file, back up over it, and type `C-M-f' to find the end of the unbalanced defun. (Then type `C-SPC C-_ C-u C-SPC' to set the mark there, undo the insertion of the open parenthesis, and finally return to the mark.) Then find the actual matching close parenthesis by typing `C-M-f' at the beginning of the defun. This will leave you somewhere short of the place where the defun ought to end. It is possible that you will find a spurious close parenthesis in that vicinity. If you don't see a problem at that point, the next thing to do is to type `C-M-q' at the beginning of the defun. A range of lines will probably shift left; if so, the missing open parenthesis or spurious close parenthesis is probably near the first of those lines. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the `C-M-q' with `C-_', since the old indentation is probably appropriate to the intended parentheses. After you think you have fixed the problem, use `C-M-q' again. If the old indentation actually fit the intended nesting of parentheses, and you have put back those parentheses, `C-M-q' should not change anything.  File: elisp, Node: Compilation Errors, Next: Edebug, Prev: Syntax Errors, Up: Debugging Debugging Problems in Compilation ================================= When an error happens during byte compilation, it is normally due to invalid syntax in the program you are compiling. The compiler prints a suitable error message in the `*Compile-Log*' buffer, and then stops. The message may state a function name in which the error was found, or it may not. Either way, here is how to find out where in the file the error occurred. What you should do is switch to the buffer ` *Compiler Input*'. (Note that the buffer name starts with a space, so it does not show up in `M-x list-buffers'.) This buffer contains the program being compiled, and point shows how far the byte compiler was able to read. If the error was due to invalid Lisp syntax, point shows exactly where the invalid syntax was *detected*. The cause of the error is not necessarily near by! Use the techniques in the previous section to find the error. If the error was detected while compiling a form that had been read successfully, then point is located at the end of the form. In this case, this technique can't localize the error precisely, but can still show you which function to check.  File: elisp, Node: Edebug, Prev: Compilation Errors, Up: Debugging Edebug ====== Edebug is a source-level debugger for Emacs Lisp programs with which you can: * Step through evaluation, stopping before and after each expression. * Set conditional or unconditional breakpoints. * Stop when a specified condition is true (the global break event). * Trace slow or fast, stopping briefly at each stop point, or at each breakpoint. * Display expression results and evaluate expressions as if outside of Edebug. * Automatically reevaluate a list of expressions and display their results each time Edebug updates the display. * Output trace info on function enter and exit. * Stop when an error occurs. * Display a backtrace, omitting Edebug's own frames. * Specify argument evaluation for macros and defining forms. * Obtain rudimentary coverage testing and frequency counts. The first three sections below should tell you enough about Edebug to enable you to use it. * Menu: * Using Edebug:: Introduction to use of Edebug. * Instrumenting:: You must instrument your code in order to debug it with Edebug. * Modes: Edebug Execution Modes. Execution modes, stopping more or less often. * Jumping:: Commands to jump to a specified place. * Misc: Edebug Misc. Miscellaneous commands. * Breakpoints:: Setting breakpoints to make the program stop. * Trapping Errors:: trapping errors with Edebug. * Views: Edebug Views. Views inside and outside of Edebug. * Eval: Edebug Eval. Evaluating expressions within Edebug. * Eval List:: Expressions whose values are displayed each time you enter Edebug. * Printing in Edebug:: Customization of printing. * Trace Buffer:: How to produce trace output in a buffer. * Coverage Testing:: How to test evaluation coverage. * The Outside Context:: Data that Edebug saves and restores. * Instrumenting Macro Calls:: Specifying how to handle macro calls. * Options: Edebug Options. Option variables for customizing Edebug.  File: elisp, Node: Using Edebug, Next: Instrumenting, Up: Edebug Using Edebug ------------ To debug a Lisp program with Edebug, you must first "instrument" the Lisp code that you want to debug. A simple way to do this is to first move point into the definition of a function or macro and then 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 which Edebug execution mode you have selected. The default execution mode is step, which does stop execution. *Note Edebug Execution Modes::. Within Edebug, you normally view an Emacs buffer showing the source of the Lisp code you are debugging. This is referred to as the "source code buffer". This buffer is temporarily read-only. 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) 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).) The special commands of Edebug are available in the source code buffer in addition to the commands of Emacs Lisp mode. 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 Edebug and return to the top-level command loop. Type `?' to display a list of all Edebug commands.  File: elisp, 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 code inserts additional code into it, to invoke Edebug at the proper places. 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'. When Edebug is about to instrument code for the first time in a session, it runs the hook `edebug-setup-hook', then sets it to `nil'. You can use this to load up Edebug specifications associated with a package you are using, but only when you also use Edebug. 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. This is possible only if Edebug knows where to find the source for that function; after loading Edebug, `eval-region' records the position of every definition it evaluates, even if not instrumenting it. See also the `i' command (*note Jumping::.), which steps into the call after instrumenting the function. Edebug knows how to instrument all the standard special forms, an interactive form with an expression argument, anonymous lambda expressions, and other defining forms. Edebug cannot know what a user-defined macro will do with the arguments of a macro call, so you must tell it; *Note Instrumenting Macro Calls::, for details. To remove instrumentation from a definition, simply reevaluate its definition in a way that does not instrument. There are two ways of evaluating forms that never instrument them: from a file with `load', and from the minibuffer with `eval-expression' (`M-ESC'). If Edebug detects a syntax error while instrumenting, it leaves point at the erroneous code and signals an `invalid-read-syntax' error. *Note Edebug Eval::, for other evaluation functions available inside of Edebug.  File: elisp, 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 far Edebug continues execution before stopping--whether it stops at each stop point, or continues to the next breakpoint, for example--and how much Edebug displays the progress of the evaluation before it stops. 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 the display 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 one second at each breakpoint, and then continue (`edebug-continue-mode'). `C' Rapid continue: move point to each breakpoint, but don't pause (`edebug-Continue-fast-mode'). `G' Go non-stop: ignore breakpoints (`edebug-Go-nonstop-mode'). You can still stop the program by typing `S', or any editing command. In general, the execution modes earlier in the above list run the program more slowly or stop sooner than the modes later in the list. 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 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 type 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. Also, defining or executing a keyboard macro outside of Edebug does not affect commands inside Edebug. This is usually an advantage. But see the `edebug-continue-kbd-macro' option (*note Edebug Options::.). 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.  File: elisp, Node: Jumping, Next: Edebug Misc, Prev: Edebug Execution Modes, Up: Edebug Jumping ------- The commands described in this section execute until they reach a specified location. All except `i' make a temporary breakpoint to establish the place to stop, then switch to go mode. Any other breakpoint reached before the intended stop point will also stop execution. *Note Breakpoints::, for the details on breakpoints. These commands 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. `h' Proceed to the stop point near where point is (`edebug-goto-here'). `f' Run the program forward over one expression (`edebug-forward-sexp'). `o' Run the program until the end of the containing sexp. `i' Step into the function or macro called by the form after point. The `h' command proceeds to the stop point near the current location if point, using a temporary breakpoint. See *Note Breakpoints::, for more about breakpoints. The `f' command runs the program forward over one expression. More precisely, it sets a temporary breakpoint at the position that `C-M-f' would reach, then executes 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. The `f' command does `forward-sexp' starting at point, rather than at the stop point, for flexibility. If you want to execute one expression *from the current stop point*, type `w' first, to move point there, and then type `f'. The `o' command continues "out of" an expression. It places a temporary breakpoint at the end of the sexp containing point. If the containing sexp is a function definition itself, `o' 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. The `i' command steps into the function or macro called by the list form after point, and stops at its first stop point. Note that the form need not be the one about to be evaluated. But if the form is a function call about to be evaluated, remember to use this command before any of the arguments are evaluated, since otherwise it will be too late. The `i' command instruments the function or macro it's supposed to step into, if it isn't instrumented already. This is convenient, but keep in mind that the function or macro remains instrumented unless you explicitly arrange to deinstrument it.  File: elisp, Node: Edebug Misc, Next: Breakpoints, Prev: Jumping, Up: Edebug Miscellaneous Edebug Commands ----------------------------- Some miscellaneous Edebug 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: elisp, Node: Breakpoints, Next: Trapping Errors, Prev: Edebug Misc, Up: Edebug Breakpoints ----------- Edebug's step mode stops execution at the next stop point reached. There are three other ways to stop Edebug execution once it has started: breakpoints, the global break condition, and source 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 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'). With a prefix argument, the breakpoint is temporary. `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 move point to the Edebug stop point of your choice, then type `b' or `u' to set or unset a breakpoint there. Unsetting a breakpoint where none has been set has no effect. Reevaluating or reinstrumenting a definition forgets all its breakpoints. A "conditional breakpoint" tests a condition each time the program gets there. Any errors that occur as a result of evaluating the condition are ignored, as if the result were `nil'. To set a conditional breakpoint, use `x', and specify the condition expression in the minibuffer. Setting a conditional breakpoint at a stop point that has a previously established conditional breakpoint puts the previous condition expression in the minibuffer so you can edit it. You can make a conditional or unconditional breakpoint "temporary" by using a prefix arg with the command to set the breakpoint. When a temporary breakpoint stops the program, it is automatically unset. 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 following point, within the same function, 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. * Source Breakpoints:: Embedding breakpoints in source code.  File: elisp, Node: Global Break Condition, Next: Source Breakpoints, Up: Breakpoints Global Break Condition ...................... A "global break condition" stops execution when a specified condition is satisfied, no matter where that may occur. Edebug evaluates the global break condition at every stop point. If it evaluates to a non-`nil' value, then execution stops or pauses depending on the execution mode, as if a breakpoint had been hit. If evaluating the condition gets an error, execution does not stop. You can set or edit the condition expression, stored in `edebug-global-break-condition', using the `X' command (`edebug-set-global-break-condition'). The global break condition is the simplest way to find where in your code some event occurs, but it makes code run much more slowly. So you should reset the condition to `nil' when not using it.  File: elisp, Node: Source Breakpoints, Prev: Global Break Condition, Up: Breakpoints Source Breakpoints .................. All breakpoints in a definition are forgotten each time you reinstrument it. To make a breakpoint that won't be forgotten, you can write a "source breakpoint", which is simply a call to the function `edebug' in your source code. 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, the call to `edebug' acts as a breakpoint. Depending on the execution mode, Edebug stops or pauses there. If no instrumented code is being executed when `edebug' is called, that function calls `debug'.  File: elisp, Node: Trapping Errors, Next: Edebug Views, Prev: Breakpoints, Up: Edebug Trapping Errors --------------- Emacs normally displays an error message when an error is signaled and not handled with `condition-case'. While Edebug is active, it normally responds to all unhandled errors. You can customize this with the options `edebug-on-error' and `edebug-on-quit'; see *Note Edebug Options::. When Edebug responds to an error, it shows the last stop point encountered before the error. 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 reference. In that case you might want to display a full backtrace (*note Edebug Misc::.). If you 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.  File: elisp, Node: Edebug Views, Next: Edebug Eval, Prev: Trapping Errors, Up: Edebug Edebug Views ------------ These Edebug commands let you view aspects of the buffer and window status that obtained before entry to Edebug. The outside window configuration is the collection of windows and contents that were in effect outside of Edebug. `v' Temporarily view the outside window configuration (`edebug-view-outside'). `p' Temporarily display the outside current buffer with point at its outside position (`edebug-bounce-point'). With a prefix argument N, pause for N 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 a different window displaying the same buffer, that window will be used instead to display the current definition in the future. `W' Toggle whether Edebug saves and restores the outside window configuration (`edebug-toggle-save-windows'). With a prefix argument, `W' 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-x X W' from the global keymap. You can view the outside window configuration with `v' or just bounce to the point in the current buffer with `p', even if it is not normally displayed. After moving point, you may wish to jump back to the stop point with `w' from a source code buffer. Each time you use `W' to turn saving *off*, Edebug forgets the saved outside window configuration--so that even if you turn saving back *on*, the current window configuration remains unchanged when you next exit Edebug (by continuing the program). 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: elisp, 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. *Note The Outside Context::, for details on this process. `e EXP RET' Evaluate expression EXP in the context outside of Edebug (`edebug-eval-expression'). That is, Edebug tries to minimize its interference with the evaluation. `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: elisp, Node: Eval List, Next: Printing 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 mode (*note Lisp Interaction: (emacs)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 contents of the buffer (`edebug-update-eval-list'). `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; but you can set up an "evaluation list" consisting of expressions to be evaluated each time execution stops. To do this, write one or more "evaluation list groups" in the evaluation list buffer. An evaluation list group consists of one or more Lisp expressions. Groups are separated by comment lines. The command `C-c C-u' (`edebug-update-eval-list') rebuilds the evaluation list, scanning the buffer and using the first expression of each group. (The idea is that the second expression of the group is the value previously computed and displayed.) Be careful not to add expressions that execute instrumented code since that would cause an infinite loop. Each entry to Edebug redisplays the evaluation list by inserting each expression in the buffer, followed by its current value. It also inserts comment lines so that each expression becomes its own group. Thus, if you type `C-c C-u' again without changing the buffer text, the evaluation list is effectively unchanged. If an error occurs during an evaluation from the evaluation list, the error message is displayed in a string as if it were the result. Therefore, expressions that 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) # ;--------------------------------------------------------------- (selected-window) # ;--------------------------------------------------------------- (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'. To add a new expression to the evaluation list, insert the expression at a suitable place, and insert a new comment line. (You need not insert dashes in the comment line--its contents don't matter.) Then type `C-c C-u'. 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: elisp, Node: Printing in Edebug, Next: Trace Buffer, Prev: Eval List, Up: Edebug Printing in Edebug ------------------ If an expression in your program produces a value containing circular list structure, you may get an error when Edebug attempts to print it. One way to cope with circular structure is to set `print-length' or `print-level' to truncate the printing. Edebug does this for you; it binds `print-length' and `print-level' to 50 if they were `nil'. (Actually, the variables `edebug-print-length' and `edebug-print-level' specify the values to use within Edebug.) *Note Output Variables::. You can also print 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'. Here is an example of code that creates a circular structure: (setq a '(x y)) (setcar a a)) Custom printing prints this as `Result: #1=(#1# y)'. The `#1=' notation labels the structure that follows it with the label `1', and the `#1#' notation references the previously labelled structure. This notation is used for any shared elements of lists or vectors. Other programs can also use custom printing; see `cust-print.el' for details.