This is Info file ../info/emacs, produced by Makeinfo-1.55 from the input file emacs.texi.  File: emacs, Node: Combining in Emerge, Next: Fine Points of Emerge, Prev: Exiting Emerge, Up: Emerge Combining the Two Versions -------------------------- Sometimes you want to keep *both* alternatives for a particular locus. To do this, use `x c', which edits the merge buffer like this: #ifdef NEW VERSION FROM A FILE #else /* NEW */ VERSION FROM B FILE #endif /* NEW */ While this example shows C preprocessor conditionals delimiting the two alternative versions, you can specify the strings you want by setting the variable `emerge-combine-versions-template' to a string of your choice. In the string, `%a' says where to put version A, and `%b' says where to put version B. The default setting, which produces the results shown above, looks like this: "#ifdef NEW\n%a#else /* NEW */\n%b#endif /* NEW */\n"  File: emacs, Node: Fine Points of Emerge, Prev: Combining in Emerge, Up: Emerge Fine Points of Emerge --------------------- During the merge, you mustn't try to edit the A and B buffers yourself. Emerge modifies them temporarily, but ultimately puts them back the way they were. You can have any number of merges going at once--just don't use any one buffer as input to more than one merge at once, since the temporary changes made in these buffers would get in each other's way. Starting Emerge can take a long time because it needs to compare the files fully. Emacs can't do anything else until `diff' finishes. Perhaps in the future someone will change Emerge to do the comparison in the background when the input files are large--then you could keep on doing other things with Emacs until Emerge gets ready to accept commands. After setting up the merge, Emerge runs the hook `emerge-startup-hook' (*note Hooks::.).  File: emacs, Node: C Mode, Next: Fortran, Prev: Emerge, Up: Programs C Mode ====== In addition to the facilities of typical programming language major modes (*note Program Modes::.), C mode has various special facilities. `M-a' `M-e' In C mode, `M-a' and `M-e' now move by complete C statements (`c-beginning-of-statement' and `c-end-of-statement'). These commands do ordinary, textual sentence motion when in or next to a comment. `M-q' `M-q' in C mode runs `c-fill-paragraph', which is designed for filling C comments. (We assume you don't want to fill the actual C code in a C program.) `C-c C-u' Move back to the containing preprocessor conditional, setting the mark at the starting point (`c-up-conditional'). A prefix argument acts as a repeat count. With a negative argument, this command moves forward to the end of the containing preprocessor conditional. When going backwards, `#elif' acts like `#else' followed by `#if'. When going forwards, `#elif' is ignored. `C-c C-n' Move forward across the next preprocessor conditional, setting the mark at the starting point (`c-forward-conditional'). `C-c C-p' Move backward across the previous preprocessor conditional, setting the at the starting point (`c-backward-conditional'). `M-x c-macro-expand' When you are debugging C code that uses macros, sometimes it is hard to figure out precisely how the macros expand. The command `M-x c-macro-expand' runs the C preprocessor and shows you what expansion results from the region. The portion of the buffer before the region is also included in preprocessing, for the sake of macros defined there, but the output from this part isn't shown. `M-x c-backslash-region' Insert or align `\' characters at the ends of the lines of the region, except for the last such line. This is useful after writing or editing a C macro definition. If a line already ends in `\', this command adjusts the amount of whitespace before it. Otherwise, it inserts a new `\'. C++ mode is like C mode, except that it understands C++ comment syntax and certain other differences between C and C++. It also has a command `M-x fill-c++-comment', which fills a paragraph made of C++ comment lines. The command `comment-region' is useful in C++ mode for commenting out several consecutive lines, or removing the commenting out of such lines. (You don't need this command with C comment syntax because you don't need to put comment delimiters on each line.) *Note Comments::.  File: emacs, Node: Fortran, Next: Asm Mode, Prev: C Mode, Up: Programs Fortran Mode ============ Fortran mode provides special motion commands for Fortran statements and subprograms, and indentation commands that understand Fortran conventions of nesting, line numbers and continuation statements. Fortran mode has it's own Auto Fill mode that breaks long lines into proper Fortran continuation lines. Special commands for comments are provided because Fortran comments are unlike those of other languages. Built-in abbrevs optionally save typing when you insert Fortran keywords. Use `M-x fortran-mode' to switch to this major mode. This command runs the hook `fortran-mode-hook' (*note Hooks::.). * Menu: * Motion: Fortran Motion. Moving point by statements or subprograms. * Indent: Fortran Indent. Indentation commands for Fortran. * Comments: Fortran Comments. Inserting and aligning comments. * Autofill: Fortran Autofill. Auto fill minor mode for Fortran. * Columns: Fortran Columns. Measuring columns for valid Fortran. * Abbrev: Fortran Abbrev. Built-in abbrevs for Fortran keywords. Fortran mode was contributed by Michael Prange. It has been updated by Stephen A. Wood who has collated the contributions and suggestions of many users.  File: emacs, Node: Fortran Motion, Next: Fortran Indent, Up: Fortran Motion Commands --------------- Fortran mode provides special commands to move by subprograms (functions and subroutines) and by statements. There is also a command to put the region around one subprogram, convenient for killing it or moving it. `C-M-a' Move to beginning of subprogram (`beginning-of-fortran-subprogram'). `C-M-e' Move to end of subprogram (`end-of-fortran-subprogram'). `C-M-h' Put point at beginning of subprogram and mark at end (`mark-fortran-subprogram'). `C-c C-n' Move to beginning of current or next statement (`fortran-next-statement'). `C-c C-p' Move to beginning of current or previous statement (`fortran-previous-statement').  File: emacs, Node: Fortran Indent, Next: Fortran Comments, Prev: Fortran Motion, Up: Fortran Fortran Indentation ------------------- Special commands and features are needed for indenting Fortran code in order to make sure various syntactic entities (line numbers, comment line indicators and continuation line flags) appear in the columns that are required for standard Fortran. * Menu: * Commands: ForIndent Commands. Commands for indenting Fortran. * Contline: ForIndent Cont. How continuation lines indent. * Numbers: ForIndent Num. How line numbers auto-indent. * Conv: ForIndent Conv. Conventions you must obey to avoid trouble. * Vars: ForIndent Vars. Variables controlling Fortran indent style.  File: emacs, Node: ForIndent Commands, Next: ForIndent Cont, Up: Fortran Indent Fortran Indentation Commands ............................ `TAB' Indent the current line (`fortran-indent-line'). `LFD' Indent the current and start a new indented line (`fortran-indent-new-line'). `M-LFD' Break the current line and set up a continuation line. `C-M-q' Indent all the lines of the subprogram point is in (`fortran-indent-subprogram'). Fortran mode redefines TAB to reindent the current line for Fortran (`fortran-indent-line'). This command indents Line numbers and continuation markers to their required columns, and independently indents the body of the statement based on its nesting in the program. The key `LFD' runs the command `fortran-indent-new-line', which reindents the current line then makes and indents a new line. This command is useful to reindent the closing statement of `do' loops and other blocks before starting a new line. The key `C-M-q' runs `fortran-indent-subprogram', a command to reindent all the lines of the Fortran subprogram (function or subroutine) containing point. The key `M-LFD' runs `fortran-split-line', which splits a line in the appropriate fashion for Fortran. In a non-comment line, the second half becomes a continuation line and is indented accordingly. In a comment line, both halves become separate comment lines.  File: emacs, Node: ForIndent Cont, Next: ForIndent Num, Prev: ForIndent Commands, Up: Fortran Indent Continuation Lines .................. Most modern Fortran compilers allow two ways of writing continuation lines. If the first non-space character on a line is in column 5, then that line is a continuation of the previous line. We call this "fixed format". (In GNU Emacs we always count columns from 0.) A line that starts with a tab character followed by any digit except `0' is also a continuation line. We call this style of continuation "tab format". Fortran mode can make either style of continuation line, but you must specify which one you prefer. The value of the variable `indent-tabs-mode' controls the choice: `nil' for fixed format, and non-`nil' for tab format. You can tell which style is presently in effect by the presence or absence of the string `Tab' in the mode line. If the text on a line starts with the conventional Fortran continuation marker `$', or if it begins with any non-whitespace character in column 5, Fortran mode treats it as a continuation line. When you indent a continuation line with TAB, it converts the line to the current continuation style. When you split a Fortran statement with `M-LFD', the continuation marker on the newline is created according to the continuation style. The setting of continuation style affects several other aspects of editing in Fortran mode. In fixed format mode, the minimum column number for the body of a statement is 6. Lines inside of Fortran blocks that are indented to larger column numbers always use only the space character for whitespace. In tab format mode, the minimum column number for the statement body is 8, and the whitespace before column 8 must always consist of one tab character. When you enter Fortran mode for an existing file, it tries to deduce the proper continuation style automatically from the file contents. The first line that begins with either a tab character or six spaces determines the choice. The variable `fortran-analyze-depth' specifies how many lines to consider (at the beginning of the file); if none of those lines indicates a style, then the variable `fortran-tab-mode-default' specifies the style. If it is `nil', that specifies fixed format, and non-`nil' specifies tab format.  File: emacs, Node: ForIndent Num, Next: ForIndent Conv, Prev: ForIndent Cont, Up: Fortran Indent Line Numbers ............ If a number is the first non-whitespace in the line, Fortran indentation assumes it is a line number and moves it to columns 0 through 4. (Columns always count from 0 in GNU Emacs.) Line numbers of four digits or less are normally indented one space. The variable `fortran-line-number-indent' controls this; it specifies the maximum indentation a line number can have. Line numbers are indented to right-justify them to end in column 4 unless that would require more than this maximum indentation. The default value of the variable is 1. Simply inserting a line number is enough to indent it according to these rules. As each digit is inserted, the indentation is recomputed. To turn off this feature, set the variable `fortran-electric-line-number' to `nil'. Then inserting line numbers is like inserting anything else.  File: emacs, Node: ForIndent Conv, Next: ForIndent Vars, Prev: ForIndent Num, Up: Fortran Indent Syntactic Conventions ..................... Fortran mode assumes that you follow certain conventions that simplify the task of understanding a Fortran program well enough to indent it properly: * Two nested `do' loops never share a `continue' statement. * Fortran keywords such as `if', `else', `then', `do' and others are written without embedded whitespace or line breaks. Fortran compilers generally ignore whitespace outside of string constants, but Fortran mode does not recognize these keywords if they are not contiguous. Constructs such as `else if' or `end do' are acceptable, but the second word should be on the same line as the first and not on a continuation line. If you fail to follow these conventions, the indentation commands may indent some lines unaesthetically. However, a correct Fortran program retains its meaning when reindented even if the conventions are not followed.  File: emacs, Node: ForIndent Vars, Prev: ForIndent Conv, Up: Fortran Indent Variables for Fortran Indentation ................................. Several additional variables control how Fortran indentation works: `fortran-do-indent' Extra indentation within each level of `do' statement (default 3). `fortran-if-indent' Extra indentation within each level of `if' statement (default 3). This value is also used for extra indentation within each level of the Fortran 90 `where' statement. `fortran-structure-indent' Extra indentation within each level of `structure', `union', or `map' statements (default 3). `fortran-continuation-indent' Extra indentation for bodies of continuation lines (default 5). `fortran-check-all-num-for-matching-do' If this is `nil', indentation assumes that each `do' statement ends on a `continue' statement. Therefore, when computing indentation for a statement other than `continue', it can save time by not checking for a `do' statement ending there. If this is non-`nil', indenting any numbered statement must check for a `do' that ends there. The default is `nil'. `fortran-blink-matching-if' If this is `t', indenting an `endif' statement moves the cursor momentarily to the matching `if' statement to show where it is. The default is `nil'. `fortran-minimum-statement-indent-fixed' Minimum indentation for fortran statements when using fixed format continuation line style. Statement bodies are never indented less than this much. The default is 6. `fortran-minimum-statement-indent-tab' Minimum indentation for fortran statements for tab format continuation line style. Statement bodies are never indented less than this much. The default is 8.  File: emacs, Node: Fortran Comments, Next: Fortran Autofill, Prev: Fortran Indent, Up: Fortran Comments -------- The usual Emacs comment commands assume that a comment can follow a line of code. In Fortran, the standard comment syntax requires an entire line to be just a comment. Therefore, Fortran mode replaces the standard Emacs comment commands and defines some new variables. Fortran mode can also handle a nonstandard comment syntax where comments start with `!' and can follow other text. Because only some Fortran compilers accept this syntax, Fortran mode will not insert such comments unless you have said in advance to do so. To do this, set the variable `comment-start' to `"!"' (*note Variables::.). `M-;' Align comment or insert new comment (`fortran-comment-indent'). `C-x ;' Applies to nonstandard `!' comments only. `C-c ;' Turn all lines of the region into comments, or (with argument) turn them back into real code (`fortran-comment-region'). `M-;' in Fortran mode is redefined as the command `fortran-comment-indent'. Like the usual `M-;' command, this recognizes any kind of existing comment and aligns its text appropriately; if there is no existing comment, a comment is inserted and aligned. But inserting and aligning comments are not the same in Fortran mode as in other modes. When a new comment must be inserted, if the current line is blank, a full-line comment is inserted. On a non-blank line, a nonstandard `!' comment is inserted if you have said you want to use them. Otherwise a full-line comment is inserted on a new line before the current line. Nonstandard `!' comments are aligned like comments in other languages, but full-line comments are different. In a standard full-line comment, the comment delimiter itself must always appear in column zero. What can be aligned is the text within the comment. You can choose from three styles of alignment by setting the variable `fortran-comment-indent-style' to one of these values: `fixed' Align the text at a fixed column, which is the sum of `fortran-comment-line-extra-indent' and the minimum statement indentation. This is the default. The minimum statement indentation is `fortran-minimum-statement-indent-fixed' for fixed format continuation line style and `fortran-minimum-statement-indent-tab' for tab format style. `relative' Align the text as if it were a line of code, but with an additional `fortran-comment-line-extra-indent' columns of indentation. `nil' Don't move text in full-line columns automatically at all. In addition, you can specify the character to be used to indent within full-line comments by setting the variable `fortran-comment-indent-char' to the single-character string you want to use. Fortran mode introduces two variables `comment-line-start' and `comment-line-start-skip' which play for full-line comments the same roles played by `comment-start' and `comment-start-skip' for ordinary text-following comments. Normally these are set properly by Fortran mode so you do not need to change them. The normal Emacs comment command `C-x ;' has not been redefined. If you use `!' comments, this command can be used with them. Otherwise it is useless in Fortran mode. The command `C-c ;' (`fortran-comment-region') turns all the lines of the region into comments by inserting the string `C$$$' at the front of each one. With a numeric argument, it turns the region back into live code by deleting `C$$$' from the front of each line in it. The string used for these comments can be controlled by setting the variable `fortran-comment-region'. Note that here we have an example of a command and a variable with the same name; these two uses of the name never conflict because in Lisp and in Emacs it is always clear from the context which one is meant.  File: emacs, Node: Fortran Autofill, Next: Fortran Columns, Prev: Fortran Comments, Up: Fortran Fortran Auto Fill Mode ---------------------- Fortran Auto Fill mode is a minor mode which automatically splits Fortran statements as you insert them when they become too wide. Splitting a statement involves making continuation lines. This splitting happens when you type SPC, RET, or TAB, and also in the Fortran indentation commands. `M-x fortran-auto-fill-mode' turns Fortran Auto Fill mode on if it was off, or off if it was on. This command works the same as `M-x auto-fill-mode' does for normal Auto Fill mode (*note Filling::.). A positive numeric argument turns Fortran Auto Fill mode on, and a negative argument turns it off. You can see when Fortran Auto Fill mode is in effect by the presence of the word `Fill' in the mode line, inside the parentheses. Fortran Auto Fill mode is a minor mode, turned on or off for each buffer individually. *Note Minor Modes::. Fortran Auto Fill mode breaks lines at spaces or delimiters when the lines get longer than the desired width (the value of `fill-column'). The delimiters that Fortran Auto Fill mode may break at are `,', `'', `+', `-', `/', `*', `=', and `)'. The line break comes after the delimiter if the variable `fortran-break-before-delimiters' is `nil'. Otherwise (and by default), the break comes before the delimiter. By default, Fortran Auto Fill mode is not enabled. If you want this feature turned on permanently, add a hook function to `fortran-mode-hook' to execute `(fortran-auto-fill-mode 1)'. *Note Hooks::.  File: emacs, Node: Fortran Columns, Next: Fortran Abbrev, Prev: Fortran Autofill, Up: Fortran Columns ------- `C-c C-r' Display a "column ruler" momentarily above the current line (`fortran-column-ruler'). `C-c C-w' Split the current window horizontally temporarily so that it is 72 columns wide. This may help you avoid making lines longer than the 72 character limit that some fortran compilers impose (`fortran-window-create-momentarily'). The command `C-c C-r' (`fortran-column-ruler') shows a column ruler momentarily above the current line. The comment ruler is two lines of text that show you the locations of columns with special significance in Fortran programs. Square brackets show the limits of the columns for line numbers, and curly brackets show the limits of the columns for the statement body. Column numbers appear above them. Note that the column numbers count from zero, as always in GNU Emacs. As a result, the numbers may be one less than those you are familiar with; but the positions they indicate in the line are standard for Fortran. The text used to display the column ruler is the value of the variable `fortran-comment-ruler'. By changing this variable, you can change the display. For even more help, use `C-c C-w' (`fortran-window-create'), a command which splits the current window horizontally, making a window 72 columns wide. By editing in this window you can immediately see when you make a line too wide to be correct Fortran.  File: emacs, Node: Fortran Abbrev, Prev: Fortran Columns, Up: Fortran Fortran Keyword Abbrevs ----------------------- Fortran mode provides many built-in abbrevs for common keywords and declarations. These are the same sort of abbrev that you can define yourself. To use them, you must turn on Abbrev mode. *Note Abbrevs::. The built-in abbrevs are unusual in one way: they all start with a semicolon. You cannot normally use semicolon in an abbrev, but Fortran mode makes this possible by changing the syntax of semicolon to "word constituent." For example, one built-in Fortran abbrev is `;c' for `continue'. If you insert `;c' and then insert a punctuation character such as a space or a newline, the `;c' expands automatically to `continue', provided Abbrev mode is enabled. Type `;?' or `;C-h' to display a list of all the built-in Fortran abbrevs and what they stand for.  File: emacs, Node: Asm Mode, Prev: Fortran, Up: Programs Asm Mode ======== Asm mode is a major mode for editing files of assembler code. It defines these commands: `TAB' `tab-to-tab-stop'. `LFD' Insert a newline and then indent using `tab-to-tab-stop'. `:' Insert a colon and then remove the indentation from before the label preceding colon. Then do `tab-to-tab-stop'. `;' Insert or align a comment. The variable `asm-comment-char' specifies which character starts comments in assembler syntax.  File: emacs, Node: Building, Next: Abbrevs, Prev: Programs, Up: Top Compiling and Testing Programs ****************************** The previous chapter discusses the Emacs commands that are useful for making changes in programs. This chapter deals with commands that assist in the larger process of developing and maintaining programs. * Menu: * Compilation:: Compiling programs in languages other than Lisp (C, Pascal, etc.) * Debuggers:: Running symbolic debuggers for non-Lisp programs. * Executing Lisp:: Various modes for editing Lisp programs, with different facilities for running the Lisp programs. * Libraries: Lisp Libraries. Creating Lisp programs to run in Emacs. * Interaction: Lisp Interaction. Executing Lisp in an Emacs buffer. * Eval: Lisp Eval. Executing a single Lisp expression in Emacs. * External Lisp:: Communicating through Emacs with a separate Lisp.  File: emacs, Node: Compilation, Next: Debuggers, Up: Building Running `make', or Compilers Generally ====================================== Emacs can run compilers for noninteractive languages such as C and Fortran as inferior processes, feeding the error log into an Emacs buffer. It can also parse the error messages and show you the source lines where compilation errors occurred. `M-x compile' Run a compiler asynchronously under Emacs, with error messages to `*compilation*' buffer. `M-x grep' Run `grep' asynchronously under Emacs, with matching lines listed in the buffer named `*grep*'. `M-x kill-compilation' `M-x kill-grep' Kill the running compilation or `grep' subprocess. `C-x `' Visit the locus of the next compiler error message or `grep' match. To run `make' or another compilation command, do `M-x compile'. This command reads a shell command line using the minibuffer, and then executes the command in an inferior shell, putting output in the buffer named `*compilation*'. The current buffer's default directory is used as the working directory for the execution of the command; normally, therefore, the compilation happens in this directory. When the shell command line is read, the minibuffer appears containing a default command line, which is the command you used the last time you did `M-x compile'. If you type just RET, the same command line is used again. For the first `M-x compile', the default is `make -k'. The default compilation command comes from the variable `compile-command'; if the appropriate compilation command for a file is something other than `make -k', it can be useful for the file to specify a local value for `compile-command' (*note File Variables::.). Starting a compilation displays the buffer `*compilation*' in another window but does not select it. The buffer's mode line tells you whether compilation is finished, with the word `run' or `exit' inside the parentheses. You do not have to keep this buffer visible; compilation continues in any case. While a compilation is going on, the string `Compiling' appears in the mode lines of all windows. When this string disappears, the compilation is finished. To kill the compilation process, do `M-x kill-compilation'. When the compiler process terminates, the mode line of the `*compilation*' buffer changes to say `signal' instead of `run'. Starting a new compilation also kills any running compilation, as only one can exist at any time. However, `M-x compile' asks for confirmation before actually killing a compilation that is running. The `*compilation*' buffer uses a special major mode, Compilation mode. This mode provides the keys SPC and DEL to scroll by screenfuls, and `M-n' and `M-p' to move to the next or previous error message. You can also use `M-{' and `M-}' to move up or down to an error message for a different source file. You can visit the source for any particular error message by moving point in `*compilation*' to that error message and typing `C-c C-c' (`compile-goto-error'). To parse the compiler error messages sequentially, type `C-x `' (`next-error'). The character following the `C-x' is the backquote or "grave accent," not the single-quote. This command is available in all buffers, not just in `*compilation*'. It displays the next error message at the top of one window and source location of the error in another window. The first time `C-x `' is used after the start of a compilation, it moves to the first error's location. Subsequent uses of `C-x `' advance down the data set up by the first use. When the preparsed error messages are exhausted, the next `C-x `' checks for any more error messages that have come in; this is useful if you start editing the compilation errors while the compilation is still going on. If no more error messages have come in, `C-x `' reports an error. `C-u C-x `' discards the preparsed error message data and parses the `*compilation*' buffer over again, then displaying the first error. This way, you can process the same set of errors again. Instead of running a compiler, you can run `grep' and see the lines on which matches were found. To do this, type `M-x grep' with an argument line that contains the same arguments you would give `grep' when running it normally: a `grep'-style regexp (usually in single-quotes to quote the shell's special characters) followed by file names which may use wildcards. The output from `grep' goes in the `*grep*' buffer and the lines that matched can be found with `C-x `' as if they were compilation errors. Note: a shell is used to run the compile command, but the shell is told that it should be noninteractive. This means in particular that the shell starts up with no prompt. If you find your usual shell prompt making an unsightly appearance in the `*compilation*' buffer, it means you have made a mistake in your shell's init file (`.cshrc' or `.shrc' or ...) by setting the prompt unconditionally. The shell init file should set the prompt only if there already is a prompt. In `csh', here is how to do it: if ($?prompt) set prompt = ...  File: emacs, Node: Debuggers, Next: Executing Lisp, Prev: Compilation, Up: Building Running Debuggers Under Emacs ============================= The GUD (Grand Unified Debugger) library provides an interface to various symbolic debuggers from within Emacs. We recommend the debugger GDB, which is free software, but you can also run DBX, SDB or XDB if you have them. * Menu: * Starting GUD:: How to start a debugger subprocess. * Debugger Operation:: Connection between the debugger and source buffers. * Commands of GUD:: Keybindings for common commands. * GUD Customization:: Defining your own commands for GUD.  File: emacs, Node: Starting GUD, Next: Debugger Operation, Up: Debuggers Starting GUD ------------ There are four commands for starting a debugger, each corresponding to a particular debugger program. `M-x gdb RET FILE RET' Run GDB as a subprocess of Emacs. This command creates a buffer for input and output to GDB, and switches to it. If a GDB buffer already exists, it just switches to that buffer. `M-x dbx RET FILE RET' Similar, but run DBX instead of GDB. `M-x xdb RET FILE RET' Similar, but run XDB instead of GDB. Use the variable `gud-xdb-directories' to specify directories to search for source files. `M-x sdb RET FILE RET' Similar, but run SDB instead of GDB. Some versions of SDB do not mention source file names in their messages. When you use them, you need to have a valid tags table (*note Tags::.) in order for GUD to find functions in the source code. If you have not visited a tags table or the tags table doesn't list one of the functions, you get a message saying `The sdb support requires a valid tags table to work'. If this happens, generate a valid tags table in the working directory and try again. You can only run one debugger process at a time. Each of these commands takes one argument: a command line to invoke the debugger. In the simplest case, specify just the name of the executable file you want to debug. You may also use options that the debugger supports. However, shell wild cards and variables are not allowed. GUD assumes that the first argument not preceded by a `-' is the executable file name.  File: emacs, Node: Debugger Operation, Next: Commands of GUD, Prev: Starting GUD, Up: Debuggers Debugger Operation ------------------ When you run a debugger with GUD, the debugger uses an Emacs buffer for its ordinary input and output. This is called the GUD buffer. The debugger uses other Emacs buffers to display the source files of the program. An arrow (`=>') in one of these buffers indicates the current execution line. Moving point in this buffer does not move the arrow. You can start editing these source files at any time in the buffers that were made to display them. The arrow is not part of the file's text; it appears only on the screen. If you do modify a source file, keep in mind that inserting or deleting lines will throw off the arrow's positioning; GUD has no way of figuring out which line corresponded before your changes to the line number in a debugger message. Also, you'll typically have to recompile and restart the program for your changes to be reflected in the debugger's tables. If you wish, you can control your debugger process entirely through the debugger buffer, which uses a variant of Shell mode. All the usual commands for your debugger are available, and you can use the Shell mode history commands to repeat them.  File: emacs, Node: Commands of GUD, Next: GUD Customization, Prev: Debugger Operation, Up: Debuggers Commands of GUD --------------- GUD provides a command available in all buffers for setting breakpoints. This command is defined globally because you need to use it in the source files' buffers. `C-x SPC' Set a breakpoint on the line that point is on. Here are the other commands provided by GUD. The keys starting with `C-c' are available only in the GUD interaction buffer. The bindings that start with `C-x C-a' are available in the GUD buffer and also in source files. `C-c C-l' `C-x C-a C-l' Display in another window the last line referred to in the GUD buffer (that is, the line indicated in the last location message). This runs the command `gud-refresh'. `C-c C-s' `C-x C-a C-s' Execute a single line of code (`gud-step'). If the code contains a function call, execution stops after entering the called function. `C-c C-n' `C-x C-a C-n' Execute a single line of code, stepping across entire function calls at full speed (`gud-next'). `C-c C-i' `C-x C-a C-i' Execute a single machine instruction (`gud-stepi'). `C-c C-c' `C-x C-a C-c' Continue execution until the next breakpoint, or other event that would normally stop the program (`gud-cont'). `C-c C-d' `C-x C-a C-d' Delete the breakpoint(s) on the current source line, if any (`gud-remove'). If you use this command in the GUD interaction buffer, it applies to the line where the program last stopped. `C-c C-t' `C-x C-a C-t' Set a temporary breakpoint on the current source line, if any. If you use this command in the GUD interaction buffer, it applies to the line where the program last stopped. The above commands are common to all supported debuggers. If you are using GDB or (some versions of) DBX, these additional commands are available: `C-c <' `C-x C-a <' Select the next enclosing stack frame (`gud-up'). This is equivalent to the `up' command. `C-c >' `C-x C-a >' Select the next inner stack frame (`gud-down'). This is equivalent to the `down' command. If you are using GDB, two additional keybindings are available: `C-c C-f' `C-x C-a C-f' Run the program until the selected stack frame returns (or until it stops for some other reason). These commands interpret a prefix argument as a repeat count, when that makes sense.  File: emacs, Node: GUD Customization, Prev: Commands of GUD, Up: Debuggers GUD Customization ----------------- On startup, GUD runs one of the following hooks: `gdb-mode-hook', if you are using GDB; `dbx-mode-hook', if you are using DBX; `sdb-mode-hook', if you are using SDB; and `xdb-mode-hook', if you are using XDB. You can use these hooks to define custom keybindings for the debugger interaction buffer. *Note Hooks::. Here is a convenient way to define a command that sends a particular command string to the debugger, and set up a key binding for it in the debugger interaction buffer: (gud-def FUNCTION CMDSTRING BINDING DOCSTRING) This defines a command named FUNCTION which sends CMDSTRING to the debugger process, with documentation string DOCSTRING. You can use the command thus defined in any buffer. If BINDING is non-`nil', `gud-def' also binds the command to `C-c BINDING' in the GUD buffer's mode and to `C-x C-a BINDING' generally. The command string CMDSTRING may contain certain escape sequences that are filled in with varying data at the time FUNCTION is called: `%f' Name of the current source file. If the current buffer is the GUD buffer, then the "current source file" is the file that the program stopped in. `%l' Number of the current source line. If the current buffer is the GUD buffer, then the "current source line" is the line that the program stopped in. `%e' Text of the C lvalue or function-call expression surrounding point. `%a' Text of the hexadecimal address surrounding point. `%p' Prefix (numeric) argument of the called function (if any) as a number. (If you don't use `%p' in the command string, the command you define ignores any prefix argument.)  File: emacs, Node: Executing Lisp, Next: Lisp Libraries, Prev: Debuggers, Up: Building Executing Lisp Expressions ========================== Emacs has several different major modes for Lisp and Scheme. They are the same in terms of editing commands, but differ in the commands for executing Lisp expressions. Emacs-Lisp mode The mode for editing source files of programs to run in Emacs Lisp. This mode defines `C-M-x' to evaluate the current defun. *Note Lisp Libraries::. Lisp Interaction mode The mode for an interactive session with Emacs Lisp. It defines LFD to evaluate the sexp before point and insert its value in the buffer. *Note Lisp Interaction::. Lisp mode The mode for editing source files of programs that run in Lisps other than Emacs Lisp. This mode defines `C-M-x' to send the current defun to an inferior Lisp process. *Note External Lisp::. Inferior Lisp mode The mode for an interactive session with an inferior Lisp process. This mode combines the special features of Lisp mode and Shell mode (*note Shell Mode::.). Scheme mode Like Lisp mode but for Scheme programs. Inferior Scheme mode The mode for an interactive session with an inferior Scheme process. * Menu: These subnodes of the chapter on editing programs describe the editing commands for working with Lisp programs, which are in fact available globally. * Lists:: Expressions with balanced parentheses. * List Commands:: The commands for working with list and sexps. * Defuns:: Each program is made up of separate functions. There are editing commands to operate on them. * Program Indent:: Adjusting indentation to show the nesting. * Matching:: Insertion of a close-delimiter flashes matching open. * Comments:: Inserting, killing, and aligning comments.  File: emacs, Node: Lisp Libraries, Next: Lisp Interaction, Prev: Executing Lisp, Up: Building Libraries of Lisp Code for Emacs ================================ Lisp code for Emacs editing commands is stored in files whose names conventionally end in `.el'. This ending tells Emacs to edit them in Emacs-Lisp mode (*note Executing Lisp::.). To execute a file of Emacs Lisp code, use `M-x load-file'. This command reads a file name using the minibuffer and then executes the contents of that file as Lisp code. It is not necessary to visit the file first; in any case, this command reads the file as found on disk, not text in an Emacs buffer. Once a file of Lisp code is installed in the Emacs Lisp library directories, users can load it using `M-x load-library'. Programs can load it by calling `load-library', or with `load', a more primitive function that is similar but accepts some additional arguments. `M-x load-library' differs from `M-x load-file' in that it searches a sequence of directories and tries three file names in each directory. Suppose your argument is LIB; the three names are `LIB.elc', `LIB.el', and lastly just `LIB'. If `LIB.elc' exists, it is by convention the result of compiling `LIB.el'; it is better to load the compiled file, since it will load and run faster. If `load-library' finds that `LIB.el' is newer than `LIB.elc' file, it prints a warning, because it's likely that somebody made changes to the `.el' file and forgot to recompile it. Because the argument to `load-library' is usually not in itself a valid file name, file name completion is not available. Indeed, when using this command, you usually do not know exactly what file name will be used. The sequence of directories searched by `M-x load-library' is specified by the variable `load-path', a list of strings that are directory names. The default value of the list contains the directory where the Lisp code for Emacs itself is stored. If you have libraries of your own, put them in a single directory and add that directory to `load-path'. `nil' in this list stands for the current default directory, but it is probably not a good idea to put `nil' in the list. If you find yourself wishing that `nil' were in the list, most likely what you really want to do is use `M-x load-file' this once. Often you do not have to give any command to load a library, because the commands defined in the library are set up to "autoload" that library. Running any of those commands causes `load' to be called to load the library; this replaces the autoload definitions with the real ones from the library. If autoloading a file does not finish, either because of an error or because of a `C-g' quit, all function definitions made by the file are undone automatically. So are any calls to `provide'. As a consequence, if you use one of the autoloadable commands again, the entire file will be loaded a second time. This prevents problems where the command is no longer autoloading but it works wrong because not all the file was loaded. Function definitions are undone only for autoloading; explicit calls to `load' do not undo anything if loading is not completed. Emacs Lisp code can be compiled into byte-code which loads faster, takes up less space when loaded, and executes faster. *Note Byte Compilation: (elisp)Byte Compilation. By convention, the compiled code for a library goes in a separate file whose name consists of the library source file with `c' appended. Thus, the compiled code for `foo.el' goes in `foo.elc'. That's why `load-library' searches for `.elc' files first.  File: emacs, Node: Lisp Eval, Next: External Lisp, Prev: Lisp Interaction, Up: Building Evaluating Emacs-Lisp Expressions ================================= Lisp programs intended to be run in Emacs should be edited in Emacs-Lisp mode; this happens automatically for file names ending in `.el'. By contrast, Lisp mode itself is used for editing Lisp programs intended for other Lisp systems. To switch to Emacs-Lisp mode explicitly, use the command `M-x emacs-lisp-mode'. For testing of Lisp programs to run in Emacs, it is often useful to evaluate part of the program as it is found in the Emacs buffer. For example, after changing the text of a Lisp function definition, evaluating the definition installs the change for future calls to the function. Evaluation of Lisp expressions is also useful in any kind of editing, for invoking noninteractive functions (functions that are not commands). `M-ESC' Read a single Lisp expression in the minibuffer, evaluate it, and print the value in the echo area (`eval-expression'). `C-x C-e' Evaluate the Lisp expression before point, and print the value in the echo area (`eval-last-sexp'). `C-M-x' Evaluate the defun containing or after point, and print the value in the echo area (`eval-defun'). `M-x eval-region' Evaluate all the Lisp expressions in the region. `M-x eval-current-buffer' Evaluate all the Lisp expressions in the buffer. `M-ESC' (`eval-expression') is the most basic command for evaluating a Lisp expression interactively. It reads the expression using the minibuffer, so you can execute any expression on a buffer regardless of what the buffer contains. When the expression is evaluated, the current buffer is once again the buffer that was current when `M-ESC' was typed. `M-ESC' can easily confuse users who do not understand it, especially on keyboards with autorepeat where it can result from holding down the ESC key for too long. Therefore, `eval-expression' is normally a disabled command. Attempting to use this command asks for confirmation and gives you the option of enabling it; once you enable the command, confirmation will no longer be required for it. *Note Disabling::. In Emacs-Lisp mode, the key `C-M-x' is bound to the command `eval-defun', which parses the defun containing or following point as a Lisp expression and evaluates it. The value is printed in the echo area. This command is convenient for installing in the Lisp environment changes that you have just made in the text of a function definition. The command `C-x C-e' (`eval-last-sexp') performs a similar job but is available in all major modes, not just Emacs-Lisp mode. It finds the sexp before point, reads it as a Lisp expression, evaluates it, and prints the value in the echo area. It is sometimes useful to type in an expression and then, with point still after it, type `C-x C-e'. If `C-M-x' or `C-x C-e' is given a numeric argument, it prints the value by insertion into the current buffer at point, rather than in the echo area. The argument value does not matter. The most general command for evaluating Lisp expressions from a buffer is `eval-region'. `M-x eval-region' parses the text of the region as one or more Lisp expressions, evaluating them one by one. `M-x eval-current-buffer' is similar but evaluates the entire buffer. This is a reasonable way to install the contents of a file of Lisp code that you are just ready to test. After finding and fixing a bug, use `C-M-x' on each function that you change, to keep the Lisp world in step with the source file.  File: emacs, Node: Lisp Interaction, Next: Lisp Eval, Prev: Lisp Libraries, Up: Building Lisp Interaction Buffers ======================== The buffer `*scratch*' which is selected when Emacs starts up is provided for evaluating Lisp expressions interactively inside Emacs. Thus, the way to use the `*scratch*' buffer is to insert Lisp expressions at the end, ending each one with LFD so that it will be evaluated. This command reads the Lisp expression before point, evaluates it, and inserts the value in printed representation before point. The result is a complete typescript of the expressions you have evaluated and their values. The `*scratch*' buffer's major mode is Lisp Interaction mode, which is the same as Emacs-Lisp mode except for the binding of LFD. The rationale for this feature is that Emacs must have a buffer when it starts up, but that buffer is not useful for editing files since a new buffer is made for every file that you visit. The Lisp interpreter typescript is the most useful thing I can think of for the initial buffer to do. Type `M-x lisp-interaction-mode' to put the current buffer in Lisp Interaction mode.