This is Info file ../../info/lispref.info, produced by Makeinfo version 1.68 from the input file lispref.texi. INFO-DIR-SECTION XEmacs Editor START-INFO-DIR-ENTRY * Lispref: (lispref). XEmacs Lisp Reference Manual. END-INFO-DIR-ENTRY 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, 20.3) v3.2, April, May, November 1997 XEmacs Lisp Reference Manual (for 21.0) v3.3, April 1998 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: 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 ' 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- EXP ' 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) # ;--------------------------------------------------------------- (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'. 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...)'.  File: lispref.info, Node: Backtracking, Next: Debugging Backquote, Prev: Specification List, Up: Instrumenting Macro Calls Backtracking ............ If a specification fails to match at some point, this does not necessarily mean a syntax error will be signaled; instead, "backtracking" will take place until all alternatives have been exhausted. Eventually every element of the argument list must be matched by some element in the specification, and every required element in the specification must match some argument. Backtracking is disabled for the remainder of a sublist or group when certain conditions occur, described below. Backtracking is reenabled when a new alternative is established by `&optional', `&rest', or `&or'. It is also reenabled initially when processing a sublist or group specification or an indirect specification. You might want to disable backtracking to commit to some alternative so that Edebug can provide a more specific syntax error message. Normally, if no alternative matches, Edebug reports that none matched, but if one alternative is committed to, Edebug can report how it failed to match. First, backtracking is disabled while matching any of the form specifications (i.e. `form', `body', `def-form', and `def-body'). These specifications will match any form so any error must be in the form itself rather than at a higher level. Second, backtracking is disabled after successfully matching a quoted symbol or string specification, since this usually indicates a recognized construct. If you have a set of alternative constructs that all begin with the same symbol, you can usually work around this constraint by factoring the symbol out of the alternatives, e.g., `["foo" &or [first case] [second case] ...]'. Third, backtracking may be explicitly disabled by using the `gate' specification. This is useful when you know that no higher alternatives may apply.  File: lispref.info, Node: Debugging Backquote, Next: Specification Examples, Prev: Backtracking, Up: Instrumenting Macro Calls Debugging Backquote ................... Backquote (``') is a macro that results in an expression that may or may not be evaluated. It is often used to simplify the definition of a macro to return an expression that is evaluated, but Edebug does not know when this is the case. However, the forms inside unquotes (`,' and `,@') are evaluated and Edebug instruments them. Nested backquotes are supported by Edebug, but there is a limit on the support of quotes inside of backquotes. Quoted forms (with `'') are not normally evaluated, but if the quoted form appears immediately within `,' and `,@' forms, Edebug treats this as a backquoted form at the next higher level (even if there is not a next higher level - this is difficult to fix). If the backquoted forms happen to be code intended to be evaluated, you can have Edebug instrument them by using `edebug-`' instead of the regular ``'. Unquoted forms can always appear inside `edebug-`' anywhere a form is normally allowed. But `(, FORM)' may be used in two other places specially recognized by Edebug: wherever a predicate specification would match, and at the head of a list form in place of a function name or lambda expression. The FORM inside a spliced unquote, `(,@ FORM)', will be wrapped, but the unquote form itself will not be wrapped since this would interfere with the splicing. There is one other complication with using `edebug-`'. If the `edebug-`' call is in a macro and the macro may be called from code that is also instrumented, and if unquoted forms contain any macro arguments bound to instrumented forms, then you should modify the specification for the macro as follows: the specifications for those arguments must use `def-form' instead of `form'. (This is to reestablish the Edebugging context for those external forms.) For example, the `for' macro (*note Problems with Macros: ()Problems with Macros.) is shown here but with `edebug-`' substituted for regular ``'. (defmacro inc (var) (list 'setq var (list '1+ var))) (defmacro for (var from init to final do &rest body) (let ((tempvar (make-symbol "max"))) (edebug-` (let (((, var) (, init)) ((, tempvar) (, final))) (while (<= (, var) (, tempvar)) (, body) (inc (, var))))))) Here is the corresponding modified Edebug specification and some code that calls the macro: (def-edebug-spec for (symbolp "from" def-form "to" def-form "do" &rest def-form)) (let ((n 5)) (for i from n to (* n (+ n 1)) do (message "%s" i))) After instrumenting the `for' macro and the macro call, Edebug first steps to the beginning of the macro call, then into the macro body, then through each of the unquoted expressions in the backquote showing the expressions that will be embedded in the backquote form. Then when the macro expansion is evaluated, Edebug will step through the `let' form and each time it gets to an unquoted form, it will jump back to an argument of the macro call to step through that expression. Finally stepping will continue after the macro call. Even more convoluted execution paths may result when using anonymous functions. When the result of an expression is an instrumented expression, it is difficult to see the expression inside the instrumentation. So you may want to set the option `edebug-unwrap-results' to a non-`nil' value while debugging such expressions, but it would slow Edebug down to always do this.  File: lispref.info, Node: Specification Examples, Prev: Debugging Backquote, Up: Instrumenting Macro Calls Specification Examples ...................... Here we provide several examples of Edebug specifications to show many of its capabilities. A `let' special form has a sequence of bindings and a body. Each of the bindings is either a symbol or a sublist with a symbol and optional value. In the specification below, notice the `gate' inside of the sublist to prevent backtracking. (def-edebug-spec let ((&rest &or symbolp (gate symbolp &optional form)) body)) Edebug uses the following specifications for `defun' and `defmacro' and the associated argument list and `interactive' specifications. It is necessary to handle the expression argument of an interactive form specially since it is actually evaluated outside of the function body. (def-edebug-spec defmacro defun) ; Indirect ref to `defun' spec (def-edebug-spec defun (&define name lambda-list [&optional stringp] ; Match the doc string, if present. [&optional ("interactive" interactive)] def-body)) (def-edebug-spec lambda-list (([&rest arg] [&optional ["&optional" arg &rest arg]] &optional ["&rest" arg] ))) (def-edebug-spec interactive (&optional &or stringp def-form)) ; Notice: `def-form' The specification for backquote below illustrates how to match dotted lists and use `nil' to terminate recursion. It also illustrates how components of a vector may be matched. (The actual specification provided by Edebug does not support dotted lists because doing so causes very deep recursion that could fail.) (def-edebug-spec ` (backquote-form)) ;; alias just for clarity (def-edebug-spec backquote-form (&or ([&or "," ",@"] &or ("quote" backquote-form) form) (backquote-form . [&or nil backquote-form]) (vector &rest backquote-form) sexp))  File: lispref.info, Node: Edebug Options, Prev: Instrumenting Macro Calls, Up: Edebug Edebug Options -------------- These options affect the behavior of Edebug: - User Option: edebug-setup-hook Functions to call before Edebug is used. Each time it is set to a new value, Edebug will call those functions once and then `edebug-setup-hook' is reset to `nil'. You could use this to load up Edebug specifications associated with a package you are using but only when you also use Edebug. See *Note Instrumenting::. - User Option: edebug-all-defs If non-`nil', normal evaluation of any defining forms (e.g. `defun' and `defmacro') will instrument them for Edebug. This applies to `eval-defun', `eval-region', and `eval-current-buffer'. Use the command `M-x edebug-all-defs' to toggle the value of this variable. You may want to make this variable local to each buffer by calling `(make-local-variable 'edebug-all-defs)' in your `emacs-lisp-mode-hook'. See *Note Instrumenting::. - User Option: edebug-all-forms If non-`nil', normal evaluation of any forms by `eval-defun', `eval-region', and `eval-current-buffer' will instrument them for Edebug. Use the command `M-x edebug-all-forms' to toggle the value of this option. See *Note Instrumenting::. - User Option: edebug-save-windows If non-`nil', save and restore window configuration on Edebug calls. It takes some time to do this, so if your program does not care what happens to data about windows, you may want to set this variable to `nil'. If the value is a list, only the listed windows are saved and restored. `M-x edebug-toggle-save-windows' may be used to change this variable. This command is bound to `W' in source code buffers. See *Note Edebug Display Update::. - User Option: edebug-save-displayed-buffer-points If non-`nil', save and restore point in all displayed buffers. This is necessary if you are debugging code that changes the point of a buffer which is displayed in a non-selected window. If Edebug or the user then selects the window, the buffer's point will be changed to the window's point. This is an expensive operation since it visits each window and therefore each displayed buffer twice for each Edebug activation, so it is best to avoid it if you can. See *Note Edebug Display Update::. - User Option: edebug-initial-mode If this variable is non-`nil', it specifies the initial execution mode for Edebug when it is first activated. Possible values are `step', `next', `go', `Go-nonstop', `trace', `Trace-fast', `continue', and `Continue-fast'. The default value is `step'. See *Note Edebug Execution Modes::. - User Option: edebug-trace Non-`nil' means display a trace of function entry and exit. Tracing output is displayed in a buffer named `*edebug-trace*', one function entry or exit per line, indented by the recursion level. The default value is `nil'. Also see `edebug-tracing'. See *Note Tracing::. - User Option: edebug-test-coverage If non-`nil', Edebug tests coverage of all expressions debugged. This is done by comparing the result of each expression with the previous result. Coverage is considered OK if two different results are found. So to sufficiently test the coverage of your code, try to execute it under conditions that evaluate all expressions more than once, and produce different results for each expression. Use `M-x edebug-display-freq-count' to display the frequency count and coverage information for a definition. See *Note Coverage Testing::. - User Option: edebug-continue-kbd-macro If non-`nil', continue defining or executing any keyboard macro that is executing outside of Edebug. Use this with caution since it is not debugged. See *Note Edebug Execution Modes::. - User Option: edebug-print-length If non-`nil', bind `print-length' to this while printing results in Edebug. The default value is `50'. See *Note Printing in Edebug::. - User Option: edebug-print-level If non-`nil', bind `print-level' to this while printing results in Edebug. The default value is `50'. - User Option: edebug-print-circle If non-`nil', bind `print-circle' to this while printing results in Edebug. The default value is `nil'. - User Option: edebug-on-error `debug-on-error' is bound to this while Edebug is active. See *Note Trapping Errors::. - User Option: edebug-on-quit `debug-on-quit' is bound to this while Edebug is active. See *Note Trapping Errors::. - User Option: edebug-unwrap-results Non-`nil' if Edebug should unwrap results of expressions. This is useful when debugging macros where the results of expressions are instrumented expressions. But don't do this when results might be circular or an infinite loop will result. See *Note Debugging Backquote::. - User Option: edebug-global-break-condition If non-`nil', an expression to test for at every stop point. If the result is non-nil, then break. Errors are ignored. See *Note Global Break Condition::.  File: lispref.info, Node: Read and Print, Next: Minibuffers, Prev: Debugging, Up: Top Reading and Printing Lisp Objects ********************************* "Printing" and "reading" are the operations of converting Lisp objects to textual form and vice versa. They use the printed representations and read syntax described in *Note Lisp Data Types::. This chapter describes the Lisp functions for reading and printing. It also describes "streams", which specify where to get the text (if reading) or where to put it (if printing). * Menu: * Streams Intro:: Overview of streams, reading and printing. * Input Streams:: Various data types that can be used as input streams. * Input Functions:: Functions to read Lisp objects from text. * Output Streams:: Various data types that can be used as output streams. * Output Functions:: Functions to print Lisp objects as text. * Output Variables:: Variables that control what the printing functions do.  File: lispref.info, Node: Streams Intro, Next: Input Streams, Up: Read and Print Introduction to Reading and Printing ==================================== "Reading" a Lisp object means parsing a Lisp expression in textual form and producing a corresponding Lisp object. This is how Lisp programs get into Lisp from files of Lisp code. We call the text the "read syntax" of the object. For example, the text `(a . 5)' is the read syntax for a cons cell whose CAR is `a' and whose CDR is the number 5. "Printing" a Lisp object means producing text that represents that object--converting the object to its printed representation. Printing the cons cell described above produces the text `(a . 5)'. Reading and printing are more or less inverse operations: printing the object that results from reading a given piece of text often produces the same text, and reading the text that results from printing an object usually produces a similar-looking object. For example, printing the symbol `foo' produces the text `foo', and reading that text returns the symbol `foo'. Printing a list whose elements are `a' and `b' produces the text `(a b)', and reading that text produces a list (but not the same list) with elements `a' and `b'. However, these two operations are not precisely inverses. There are three kinds of exceptions: * Printing can produce text that cannot be read. For example, buffers, windows, frames, subprocesses and markers print into text that starts with `#'; if you try to read this text, you get an error. There is no way to read those data types. * One object can have multiple textual representations. For example, `1' and `01' represent the same integer, and `(a b)' and `(a . (b))' represent the same list. Reading will accept any of the alternatives, but printing must choose one of them. * Comments can appear at certain points in the middle of an object's read sequence without affecting the result of reading it.