code:
@node Buffers, Windows, Files, Top
@chapter Using Multiple Buffers

@cindex buffers
  Text you are editing in Emacs resides in an object called a
@dfn{buffer}.  Each time you visit a file, Emacs creates a buffer to
hold the file's text.  Each time you invoke Dired, Emacs creates a buffer
to hold the directory listing.  If you send a message with @kbd{C-x m},
a buffer named @samp{*mail*} is used to hold the text of the message.
When you ask for a command's documentation, it appears in a buffer
called @samp{*Help*}.

@cindex selected buffer
@cindex current buffer
  At any time, one and only one buffer is @dfn{selected}.  It is also
called the @dfn{current buffer}.  Saying a command operates on ``the
buffer'' really means that the command operates on the selected
buffer, as most commands do.

  When Emacs creates multiple windows, each window has a chosen buffer which
is displayed there, but at any time only one of the windows is selected and
its chosen buffer is the selected buffer.  Each window's mode line displays
the name of the buffer the window is displaying (@pxref{Windows}).

  Each buffer has a name which can be of any length but is
case-sensitive.  You can select a buffer using its name.  Most
buffers are created when you visit files; their names are derived from
the files' names.  You can also create an empty buffer with any name you
want.  A newly started Emacs has a buffer named @samp{*scratch*} which
you can use for evaluating Lisp expressions in Emacs.

  Each buffer records what file it is visiting, whether it is
modified, and what major mode and minor modes are in effect in it
(@pxref{Major Modes}).  Any Emacs variable can be made @dfn{local to} a
particular buffer, meaning its value in that buffer can be different from
the value in other buffers.  @xref{Locals}.

@menu
* Select Buffer::   Creating a new buffer or reselecting an old one.
* List Buffers::    Getting a list of buffers that exist.
* Misc Buffer::     Renaming; changing read-onliness; copying text.
* Kill Buffer::     Killing buffers you no longer need.
* Several Buffers:: How to go through the list of all buffers
                     and operate variously on several of them.
@end menu

@node Select Buffer, List Buffers, Buffers, Buffers
@section Creating and Selecting Buffers
@cindex changing buffers
@cindex switching buffers

@table @kbd
@item C-x b @var{buffer} @key{RET}
Select or create a buffer named @var{buffer} (@code{switch-to-buffer}).
@item C-x 4 b @var{buffer} @key{RET}
Similar, but select a buffer named @var{buffer} in another window
(@code{switch-to-buffer-other-window}).
@item M-x switch-to-other-buffer @var{n}
Switch to the previous buffer.
@end table

@kindex C-x 4 b
@kindex C-x 5 b
@findex switch-to-buffer-other-window
@kindex C-x b
@findex switch-to-buffer
@findex switch-to-buffer-other-frame
  To select a buffer named @var{bufname}, type @kbd{C-x b @var{bufname}
@key{RET}}.  This is the command @code{switch-to-buffer} with argument
@var{bufname}.  You can use completion on an abbreviation for the buffer
name you want (@pxref{Completion}).  An empty argument to @kbd{C-x b}
specifies the most recently selected buffer that is not displayed in any
window.@refill

  Most buffers are created when you visit files, or use Emacs commands
that display text.  You can also create a buffer explicitly by typing
@kbd{C-x b @var{bufname} @key{RET}}, which creates a new, empty buffer
that is not visiting any file, and selects it for editing.  The new
buffer's major mode is determined by the value of
@code{default-major-mode} (@pxref{Major Modes}).  Buffers not visiting
files are usually used for making notes to yourself.  If you try to save
one, you are asked for the file name to use.

 The function @code{switch-to-buffer-other-frame} is similar to
@code{switch-to-buffer} except that it creates a new frame in which to
display the selected buffer.

@findex switch-to-other-buffer
Use @kbd{M-x switch-to-other-buffer} to visit the previous buffer. If
you supply a positive integer @var{n}, the @var{n}th most recent buffer
is displayed. If you supply an argument of 0, the current buffer is
moved to the bottom of the buffer stack.

  Note that you can also use @kbd{C-x C-f} and any other command for
visiting a file to switch buffers.  @xref{Visiting}.

@node List Buffers, Misc Buffer, Select Buffer, Buffers
@section Listing Existing Buffers

@table @kbd
@item C-x C-b
List the existing buffers (@code{list-buffers}).
@end table

@kindex C-x C-b
@findex list-buffers
  To print a list of all existing buffers, type @kbd{C-x C-b}.  Each
line in the list shows one buffer's name, major mode, and visited file.
A @samp{*} at the beginning of a line indicates the buffer has been
``modified''.  If several buffers are modified, it may be time to save
some with @kbd{C-x s} (@pxref{Saving}).  A @samp{%} indicates a read-only
buffer.  A @samp{.} marks the selected buffer.  Here is an example of a
buffer list:@refill

@smallexample
 MR Buffer         Size  Mode           File
 -- ------         ----  ----           ----
.*  emacs.tex      383402 Texinfo       /u2/emacs/man/emacs.tex
    *Help*         1287  Fundamental
    files.el       23076 Emacs-Lisp     /u2/emacs/lisp/files.el
  % RMAIL          64042 RMAIL          /u/rms/RMAIL
 *% man            747   Dired          /u2/emacs/man/
    net.emacs      343885 Fundamental   /u/rms/net.emacs
    fileio.c       27691 C              /u2/emacs/src/fileio.c
    NEWS           67340 Text           /u2/emacs/etc/NEWS
    *scratch*      0     Lisp Interaction
@end smallexample

@noindent
Note that the buffer @samp{*Help*} was made by a help request; it is not
visiting any file.  The buffer @code{man} was made by Dired on the
directory @file{/u2/emacs/man/}.

As you move the mouse over the @samp{*Buffer List*} buffer, the lines
are highlighted.  This visual cue indicates that clicking the right
mouse button (@code{button3}) will pop up a menu of commands on the
buffer represented by this line.  This menu duplicates most of those
commands which are bound to keys in the @samp{*Buffer List*} buffer.

@node Misc Buffer, Kill Buffer, List Buffers, Buffers
@section Miscellaneous Buffer Operations

@table @kbd
@item C-x C-q
Toggle read-only status of buffer (@code{toggle-read-only}).
@item M-x rename-buffer
Change the name of the current buffer.
@item M-x view-buffer
Scroll through a buffer.
@end table

@cindex read-only buffer
@kindex C-x C-q
@findex toggle-read-only
@vindex buffer-read-only
  A buffer can be @dfn{read-only}, which means that commands to change
its text are not allowed.  Normally, read-only buffers are created by
subsystems such as Dired and Rmail that have special commands to operate
on the text.  Emacs also creates a read-only buffer if you
visit a file that is protected.  To make changes in a read-only buffer,
use the command @kbd{C-x C-q} (@code{toggle-read-only}).  It makes a
read-only buffer writable, and makes a writable buffer read-only.  This
works by setting the variable @code{buffer-read-only}, which has a local
value in each buffer and makes a buffer read-only if its value is
non-@code{nil}.

@findex rename-buffer
  @kbd{M-x rename-buffer} changes the name of the current buffer,
prompting for the new name in the minibuffer.  There is no default.  If you
specify a name that is used by a different buffer, an error is signalled and
renaming is not done.

@findex view-buffer
  @kbd{M-x view-buffer} is similar to @kbd{M-x view-file} (@pxref{Misc
File Ops}), but it examines an already existing Emacs buffer.  View mode
provides convenient commands for scrolling through the buffer but not
for changing it.  When you exit View mode, the resulting value of point
remains in effect.

To copy text from one buffer to another, use the commands @kbd{M-x
append-to-buffer} and @kbd{M-x insert-buffer}.  @xref{Accumulating
Text}.@refill

@node Kill Buffer, Several Buffers, Misc Buffer, Buffers
@section Killing Buffers

  After using Emacs for a while, you may accumulate a large number of
buffers and may want to eliminate the ones you no
longer need.  There are several commands for doing this.

@c WideCommands
@table @kbd
@item C-x k
Kill a buffer, specified by name (@code{kill-buffer}).
@item M-x kill-some-buffers
Offer to kill each buffer, one by one.
@end table

@findex kill-buffer
@findex kill-some-buffers
@kindex C-x k

  @kbd{C-x k} (@code{kill-buffer}) kills one buffer, whose name you
specify in the minibuffer.  If you type just @key{RET} in the
minibuffer, the default, killing the current buffer, is used.  If the
current buffer is killed, the buffer that has been selected recently but
does not appear in any window now is selected.  If the buffer being
killed contains unsaved changes, you are asked to confirm with @kbd{yes}
before the buffer is killed.

  The command @kbd{M-x kill-some-buffers} asks about each buffer, one by
one.  An answer of @kbd{y} means to kill the buffer.  Killing the current
buffer or a buffer containing unsaved changes selects a new buffer or asks
for confirmation just like @code{kill-buffer}.

@node Several Buffers,, Kill Buffer, Buffers
@section Operating on Several Buffers
@cindex buffer menu

  The @dfn{buffer-menu} facility is like a ``Dired for buffers''; it allows
you to request operations on various Emacs buffers by editing a
buffer containing a list of them.  You can save buffers, kill them
(here called @dfn{deleting} them, for consistency with Dired), or display
them.

@table @kbd
@item M-x buffer-menu
Begin editing a buffer listing all Emacs buffers.
@end table

@findex buffer-menu
  The command @code{buffer-menu} writes a list of all Emacs buffers into
the buffer @samp{*Buffer List*}, and selects that buffer in Buffer Menu
mode.  The buffer is read-only.  You can only change it using the special
commands described in this section.  Most of the commands are graphic
characters.  You can use  Emacs cursor motion commands in the
@samp{*Buffer List*} buffer.  If the cursor is on a line describing a
buffer, the following  special commands apply to that buffer:

@table @kbd
@item d
Request to delete (kill) the buffer, then move down.  A @samp{D} before
the buffer name on a line indicates a deletion request.  Requested
deletions actually take place when you use the @kbd{x} command.
@item k
Synonym for @kbd{d}.
@item C-d
Like @kbd{d} but move up afterwards instead of down.
@item s
Request to save the buffer.  An @samp{S} before the buffer name on a line
indicates the request.  Requested saves actually take place when you use
the @kbd{x} command.  You can request both saving and deletion for the
same buffer.
@item ~
Mark buffer ``unmodified''.  The command @kbd{~} does this
immediately when typed.
@item x
Perform previously requested deletions and saves.
@item u
Remove any request made for the current line, and move down.
@item @key{DEL}
Move to previous line and remove any request made for that line.
@end table

  All commands that add or remove flags to request later operations
also move down a line.  They accept a numeric argument as a repeat count,
unless otherwise specified.

  There are also special commands to use the buffer list to select another
buffer, and to specify one or more other buffers for display in additional
windows.

@table @kbd
@item 1
Select the buffer in a full-frame window.  This command takes effect
immediately.
@item 2
Immediately set up two windows, with this buffer in one and the
buffer selected before @samp{*Buffer List*} in the other.
@item f
Immediately select the buffer in place of the @samp{*Buffer List*} buffer.
@item o
Immediately select the buffer in another window as if by @kbd{C-x 4 b},
leaving @samp{*Buffer List*} visible.
@item q
Immediately select this buffer, and display any buffers previously
flagged with the @kbd{m} command in other windows.  If there are no
buffers flagged with @kbd{m}, this command is equivalent to @kbd{1}.
@item m
Flag this buffer to be displayed in another window if the @kbd{q}
command is used.  The request shows as a @samp{>} at the beginning of
the line.  The same buffer may not have both a delete request and a
display request.
@end table

 Going back between a @code{buffer-menu} buffer and other Emacs buffers is
easy.  You can, for example, switch from the @samp{*Buffer List*}
buffer to another Emacs buffer, and edit there.  You can then reselect the
@code{buffer-menu} buffer and perform operations already
requested, or you can kill that buffer or pay no further attention to it.
 All that @code{buffer-menu} does directly is create and select a
suitable buffer, and turn on Buffer Menu mode.  All the other
capabilities of the buffer menu are implemented by special commands
provided in Buffer Menu mode.

  The only difference between @code{buffer-menu} and @code{list-buffers} is
that @code{buffer-menu} selects the @samp{*Buffer List*} buffer and
@code{list-buffers} does not.  If you run @code{list-buffers} (that is,
type @kbd{C-x C-b}) and select the buffer list manually, you can use all
the commands described here.


code:
@node Running, Abbrevs, Programs, Top
@chapter 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.)
* Modes: Lisp Modes.   Various modes for editing Lisp programs, with
                       different facilities for running the Lisp programs.
* Libraries: Lisp Libraries.      Creating Lisp programs to run in Emacs.
* Eval: Lisp Eval.     Executing a single Lisp expression in Emacs.
* Debug: Lisp Debug.   Debugging Lisp programs running in Emacs.
* Interaction: Lisp Interaction.  Executing Lisp in an Emacs buffer.
* External Lisp::      Communicating through Emacs with a separate Lisp.
@end menu

@node Compilation, Lisp Modes, Running, Running
@section Running ``make'', or Compilers Generally
@cindex inferior process
@cindex make
@cindex compilation errors
@cindex error log

  Emacs can run compilers for non-interactive languages like C and
Fortran as inferior processes, feeding the error log into an Emacs buffer.
It can also parse the error messages and visit the files in which errors
are found, moving point to the line where the error occurred.

@table @kbd
@item M-x compile
Run a compiler asynchronously under Emacs, with error messages to
@samp{*compilation*} buffer.
@item M-x grep
Run @code{grep} asynchronously under Emacs, with matching lines
listed in the buffer named @samp{*compilation*}.
@item M-x kill-compilation
Kill the process made by the @code{M-x compile} command.
@item M-x kill-grep
Kill the running compilation or @code{grep} subprocess.
@item C-x `
Visit the next compiler error message or @code{grep} match.
@end table

@findex compile
  To run @code{make} or another compiler, type @kbd{M-x compile}.  This
command reads a shell command line using the minibuffer, then executes
the specified command line in an inferior shell with output going to the
buffer named @samp{*compilation*}.  By default, the current buffer's
default directory is used as the working directory for the execution of
the command; therefore, the makefile comes from this directory.

@vindex compile-command
  When the shell command line is read, the minibuffer appears containing a
default command line (the command you used the last time you typed
@kbd{M-x compile}).  If you type just @key{RET}, the same command line is used
again.  The first @kbd{M-x compile} provides @code{make -k} as the default.
The default is taken from the variable @code{compile-command}; if the
appropriate compilation command for a file is something other than
@code{make -k}, it can be useful to have the file specify a local value for
@code{compile-command} (@pxref{File Variables}).

@cindex compiling files
  When you start a compilation, the buffer @samp{*compilation*} is
displayed in another window but not selected.  Its mode line displays
the word @samp{run} or @samp{exit} in the parentheses to tell you whether
compilation is finished.  You do not have to keep this buffer visible;
compilation continues in any case.

@findex kill-compilation
  To kill the compilation process, type @kbd{M-x kill-compilation}.  The mode
line of the @samp{*compilation*} buffer changes to say @samp{signal}
instead of @samp{run}.  Starting a new compilation also kills any
running compilation, as only one can occur at any time.  Starting a new
compilation prompts for confirmation before actually killing a
compilation that is running.@refill

@kindex C-x `
@findex next-error
  To parse the compiler error messages, type @kbd{C-x `}
(@code{next-error}).  The character following @kbd{C-x} is the grave
accent, not the single quote.  The command displays the buffer
@samp{*compilation*} in one window and the buffer in which the next
error occurred in another window.  Point in that buffer is moved to the
line where the error was found.  The corresponding error message is
scrolled to the top of the window in which @samp{*compilation*} is
displayed.

  The first time you use @kbd{C-x `} after the start of a compilation, it
parses all the error messages, visits all the files that have error
messages, and creates markers pointing at the lines the error messages
refer to.  It then moves to the first error message location.  Subsequent
uses of @kbd{C-x `} advance down the data set up by the first use.  When
the preparsed error messages are exhausted, the next @kbd{C-x `} checks for
any more error messages that have come in; this is useful if you start
editing compiler errors while compilation is still going on.  If no
additional error messages have come in, @kbd{C-x `} reports an error.

  @kbd{C-u C-x `} discards the preparsed error message data and parses the
@samp{*compilation*} buffer again, then displays the first error.
This way, you can process the same set of errors again.

  Instead of running a compiler, you can run @code{grep} and see the
lines on which matches were found.  To do this, type @kbd{M-x grep} with
an argument line that contains the same arguments you would give to
@code{grep}: a @code{grep}-style regexp (usually in single quotes to
quote the shell's special characters) followed by filenames, which may
use wildcard characters.  The output from @code{grep} goes in the
@samp{*compilation*} buffer.  You can use @kbd{C-x `} to find the lines that
match as if they were compilation errors.

  Note: a shell is used to run the compile command, but the shell is not
run in interactive mode.  In particular, this means that the shell starts
up with no prompt.  If you find your usual shell prompt making an
unsightly appearance in the @samp{*compilation*} buffer, it means you
have made a mistake in your shell's initialization file (@file{.cshrc}
or @file{.shrc} or @dots{}) by setting the prompt unconditionally.  The
shell initialization file should set the prompt only if there already is
a prompt.  Here's how to do it in @code{csh}:

@example
if ($?prompt) set prompt = ...
@end example

@node Lisp Modes, Lisp Libraries, Compilation, Running
@section Major Modes for Lisp

  Emacs has four different major modes for Lisp.  They are the same in
terms of editing commands, but differ in the commands for executing Lisp
expressions.

@table @asis
@item Emacs-Lisp mode
The mode for editing source files of programs to run in Emacs Lisp.
This mode defines @kbd{C-M-x} to evaluate the current defun.
@xref{Lisp Libraries}.
@item Lisp Interaction mode
The mode for an interactive session with Emacs Lisp.  It defines
@key{LFD} to evaluate the sexp before point and insert its value in the
buffer.  @xref{Lisp Interaction}.
@item Lisp mode
The mode for editing source files of programs that run in other dialects
of Lisp than Emacs Lisp.  This mode defines @kbd{C-M-x} to send the
current defun to an inferior Lisp process.  @xref{External Lisp}.
@item 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
(@pxref{Shell Mode}).
@item Scheme mode
Like Lisp mode but for Scheme programs.
@item Inferior Scheme mode
The mode for an interactive session with an inferior Scheme process.
@end table

@node Lisp Libraries, Lisp Eval, Lisp Modes, Running
@section Libraries of Lisp Code for Emacs
@cindex libraries
@cindex loading Lisp code

  Lisp code for Emacs editing commands is stored in files whose names
conventionally end in @file{.el}.  This ending tells Emacs to edit them in
Emacs-Lisp mode (@pxref{Lisp Modes}).

@menu
* Loading::		Loading libraries of Lisp code into Emacs for use.
* Compiling Libraries:: Compiling a library makes it load and run faster.
* Mocklisp::		Converting Mocklisp to Lisp so XEmacs can run it.
@end menu

@node Loading, Compiling Libraries, Lisp Libraries, Lisp Libraries
@subsection Loading Libraries

@table @kbd
@item M-x load-file @var{file}
Load the file @var{file} of Lisp code.
@item M-x load-library @var{library}
Load the library named @var{library}.
@item M-x locate-library @var{library} &optional @var{nosuffix}
Show the full path name of Emacs library @var{library}.
@end table

@findex load-file
  To execute a file of Emacs Lisp, use @kbd{M-x load-file}.  This
command reads the file name you provide in the minibuffer, then executes
the contents of that file as Lisp code.  It is not necessary to visit
the file first; in fact, this command reads the file as found on
disk, not the text in an Emacs buffer.

@findex load
@findex load-library
  Once a file of Lisp code is installed in the Emacs Lisp library
directories, users can load it using @kbd{M-x load-library}.  Programs can
load it by calling @code{load-library}, or with @code{load}, a more primitive
function that is similar but accepts some additional arguments.

  @kbd{M-x load-library} differs from @kbd{M-x load-file} in that it
searches a sequence of directories and tries three file names in each
directory.  The three names are: first, the specified name with @file{.elc}
appended; second, the name with @file{.el} appended; third, the specified
name alone.  A @file{.elc} file would be the result of compiling the Lisp
file into byte code;  if possible, it is loaded in preference to the Lisp
file itself because the compiled file loads and runs faster.

@cindex loading libraries
  Because the argument to @code{load-library} is usually not in itself
a valid file name, file name completion is not available.  In fact, when
using this command, you usually do not know exactly what file name
will be used.

@vindex load-path
  The sequence of directories searched by @kbd{M-x load-library} is
specified by the variable @code{load-path}, a list of strings that are
directory names.  The elements of this list may not begin with "@samp{~}",
so you must call @code{expand-file-name} on them before adding them to
the list.  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
@code{load-path}.  @code{nil} in this list stands for the current
default directory, but it is probably not a good idea to put @code{nil}
in the list.  If you start wishing that @code{nil} were in the list, you
should probably use @kbd{M-x load-file} for this case.

The variable is initialized by the @b{EMACSLOADPATH} environment
variable. If no value is specified, the variable takes the default value
specified in the file @file{paths.h} when Emacs was built. If a path
isn't specified in @file{paths.h}, a default value is obtained from the
file system, near the directory in which the Emacs executable resides.

@findex locate-library
 Like @kbd{M-x load-library}, @kbd{M-x locate-library} searches the
directories in @code{load-path} to find the file that @kbd{M-x load-library}
would load.  If the optional second argument @var{nosuffix} is
non-@code{nil}, the suffixes @file{.elc} or @file{.el} are not added to
the specified name @var{library} (like calling @code{load} instead of
@code{load-library}).

@cindex autoload
   You often do not have to give any command to load a library, because the
commands defined in the library are set up to @dfn{autoload} that library.
Running any of those commands causes @code{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 @kbd{C-g} quit, all function definitions made by the file
are undone automatically.  So are any calls to @code{provide}.  As a
consequence, the entire file is loaded a second time if you use one of
the autoloadable commands again.  This prevents problems when the
command is no longer autoloading but is working incorrectly because the file
was only partially loaded.  Function definitions are undone only for
autoloading; explicit calls to @code{load} do not undo anything if
loading is not completed.

@vindex after-load-alist
The variable @code{after-load-alist} takes an alist of expressions to be
evaluated when particular files are loaded.  Each element has the form
@code{(@var{filename} forms...)}.  When @code{load} is run and the filename
argument is @var{filename}, the forms in the corresponding element are
executed at the end of loading.

@var{filename} must match exactly.  Normally @var{filename} is the
name of a library, with no directory specified, since that is how load
is normally called.  An error in @code{forms} does not undo the load, but
it does prevent execution of the rest of the @code{forms}.

@node Compiling Libraries, Mocklisp, Loading, Lisp Libraries
@subsection Compiling Libraries

@cindex byte code
  Emacs Lisp code can be compiled into byte-code which loads faster,
takes up less space when loaded, and executes faster.

@table @kbd
@item M-x batch-byte-compile
Run byte-compile-file on the files remaining on the command line.
@item M-x byte-compile-buffer &optional @var{buffer}
Byte-compile and evaluate contents of @var{buffer} (default is current
buffer).
@item M-x byte-compile-file
Compile a file of Lisp code named @var{filename} into a file of byte code.
@item M-x byte-compile-and-load-file @var{filename}
Compile a file of Lisp code named @var{filename} into a file of byte
code and load it.
@item M-x byte-recompile-directory @var{directory}
Recompile every @file{.el} file in @var{directory} that needs recompilation.
@item M-x disassemble
Print disassembled code for @var{object} on (optional) @var{stream}.
@findex make-obsolete
@item M-x make-obsolete @var{function new}
Make the byte-compiler warn that @var{function} is obsolete and @var{new}
should be used instead.
@end table

@findex byte-compile-file
@findex byte-compile-and-load-file
@findex byte-compile-buffer
 @kbd{byte-compile-file} creates a byte-code compiled file from an
Emacs-Lisp source file.  The default argument for this function is the
file visited in the current buffer.  The function reads the specified
file, compiles it into byte code, and writes an output file whose name
is made by appending @file{c} to the input file name.  Thus, the file
@file{rmail.el} would be compiled into @file{rmail.elc}. To compile a
file of Lisp code named @var{filename} into a file of byte code and
then load it, use @code{byte-compile-and-load-file}. To compile and
evaluate Lisp code in a given buffer, use @code{byte-compile-buffer}.

@findex byte-recompile-directory
  To recompile all changed Lisp files in a directory, use @kbd{M-x
byte-recompile-directory}.  Specify just the directory name as an argument.
Each @file{.el} file that has been byte-compiled before is byte-compiled
again if it has changed since the previous compilation.  A numeric argument
to this command tells it to offer to compile each @file{.el} file that has
not been compiled yet.  You must answer @kbd{y} or @kbd{n} to each
offer.

@findex batch-byte-compile
  You can use the function @code{batch-byte-compile} to invoke Emacs
non-interactively from the shell to do byte compilation.  When you use
this function, the files to be compiled are specified with command-line
arguments.  Use a shell command of the form:

@example
emacs -batch -f batch-byte-compile @var{files}...
@end example

  Directory names may also be given as arguments; in that case,
@code{byte-recompile-directory} is invoked on each such directory.
@code{batch-byte-compile} uses all remaining command-line arguments as
file or directory names, then kills the Emacs process.

@findex disassemble
  @kbd{M-x disassemble} explains the result of byte compilation.  Its
argument is a function name.  It displays the byte-compiled code in a help
window in symbolic form, one instruction per line.  If the instruction
refers to a variable or constant, that is shown, too.

@node Mocklisp,,Compiling Libraries,Lisp Libraries
@subsection Converting Mocklisp to Lisp

@cindex mocklisp
@findex convert-mocklisp-buffer
  XEmacs can run Mocklisp files by converting them to Emacs Lisp first.
To convert a Mocklisp file, visit it and then type @kbd{M-x
convert-mocklisp-buffer}.  Then save the resulting buffer of Lisp file in a
file whose name ends in @file{.el} and use the new file as a Lisp library.

  You cannot currently byte-compile converted Mocklisp code.
The reason is that converted Mocklisp code uses some special Lisp features
to deal with Mocklisp's incompatible ideas of how arguments are evaluated
and which values signify ``true'' or ``false''.

@node Lisp Eval, Lisp Debug, Lisp Libraries, Running
@section Evaluating Emacs-Lisp Expressions
@cindex Emacs-Lisp mode

@findex emacs-lisp-mode
  Lisp programs intended to be run in Emacs should be edited in
Emacs-Lisp mode; this will happen automatically for file names ending in
@file{.el}.  By contrast, Lisp mode itself should be used for editing
Lisp programs intended for other Lisp systems.  Emacs-Lisp mode can be
selected with the command @kbd{M-x emacs-lisp-mode}.

  For testing of Lisp programs to run in Emacs, it is useful to be able
to evaluate part of the program as it is found in the Emacs buffer.  For
example, if you change the text of a Lisp function definition and then
evaluate the definition, Emacs installs the change for future calls to the
function.  Evaluation of Lisp expressions is also useful in any kind of
editing task for invoking non-interactive functions (functions that are
not commands).

@table @kbd
@item M-:
Read a Lisp expression in the minibuffer, evaluate it, and print the
value in the minibuffer (@code{eval-expression}).
@item C-x C-e
Evaluate the Lisp expression before point, and print the value in the
minibuffer (@code{eval-last-sexp}).
@item C-M-x
Evaluate the defun containing point or after point, and print the value in
the minibuffer (@code{eval-defun}).
@item M-x eval-region
Evaluate all the Lisp expressions in the region.
@item M-x eval-current-buffer
Evaluate all the Lisp expressions in the buffer.
@end table

@kindex M-:
@findex eval-expression
  @kbd{M-:} (@code{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 evaluation is complete,
the current buffer is once again the buffer that was current when
@kbd{M-:} was typed.

@kindex C-M-x
@findex eval-defun
  In Emacs-Lisp mode, the key @kbd{C-M-x} is bound to the function
@code{eval-defun}, which parses the defun containing point 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.

@kindex C-x C-e
@findex eval-last-sexp
  The command @kbd{C-x C-e} (@code{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 @kbd{C-x C-e}.

  If @kbd{C-M-x} or @kbd{C-x C-e} are given a numeric argument, they
print the value by inserting it into the current buffer at point, rather
than in the echo area.  The argument value does not matter.

@findex eval-region
@findex eval-current-buffer
  The most general command for evaluating Lisp expressions from a buffer
is @code{eval-region}.  @kbd{M-x eval-region} parses the text of the
region as one or more Lisp expressions, evaluating them one by one.
@kbd{M-x eval-current-buffer} is similar, but it 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 @kbd{C-M-x} on each function that you change, to keep the Lisp
world in step with the source file.

@node Lisp Debug, Lisp Interaction, Lisp Eval, Running
@section The Emacs-Lisp Debugger
@cindex debugger

@vindex debug-on-error
@vindex debug-on-quit
  XEmacs contains a debugger for Lisp programs executing inside it.
This debugger is normally not used; many commands frequently get Lisp
errors when invoked in inappropriate contexts (such as @kbd{C-f} at the
end of the buffer) and it would be unpleasant to enter a special
debugging mode in this case.  When you want to make Lisp errors invoke
the debugger, you must set the variable @code{debug-on-error} to
non-@code{nil}.  Quitting with @kbd{C-g} is not considered an error, and
@code{debug-on-error} has no effect on the handling of @kbd{C-g}.
However, if you set @code{debug-on-quit} to be non-@code{nil}, @kbd{C-g} will
invoke the debugger.  This can be useful for debugging an infinite loop;
type @kbd{C-g} once the loop has had time to reach its steady state.
@code{debug-on-quit} has no effect on errors.@refill

@findex debug-on-entry
@findex cancel-debug-on-entry
@findex debug
  You can make Emacs enter the debugger when a specified function
is called or at a particular place in Lisp code.  Use @kbd{M-x
debug-on-entry} with argument @var{fun-name} to have Emacs enter the
debugger as soon as @var{fun-name} is called. Use
@kbd{M-x cancel-debug-on-entry} to make the function stop entering the
debugger when called.  (Redefining the function also does this.)  To enter
the debugger from some other place in Lisp code, you must insert the
expression @code{(debug)} there and install the changed code with
@kbd{C-M-x}.  @xref{Lisp Eval}.@refill

  When the debugger is entered, it displays the previously selected buffer
in one window and a buffer named @samp{*Backtrace*} in another window.  The
backtrace buffer contains one line for each level of Lisp function
execution currently going on.  At the beginning of the buffer is a message
describing the reason that the debugger was invoked, for example, an
error message if it was invoked due to an error.

  The backtrace buffer is read-only and is in Backtrace mode, a special
major mode in which letters are defined as debugger commands.  The
usual Emacs editing commands are available; you can switch windows to
examine the buffer that was being edited at the time of the error, and
you can switch buffers, visit files, and perform any other editing
operations.  However, the debugger is a recursive editing level
(@pxref{Recursive Edit}); it is a good idea to return to the backtrace
buffer and explicitly exit the debugger when you don't want to use it any
more.  Exiting the debugger kills the backtrace buffer.

@cindex current stack frame
  The contents of the backtrace buffer show you the functions that are
executing and the arguments that were given to them.  It also allows you
to specify a stack frame by moving point to the line describing that
frame.  The frame whose line point is on is considered the @dfn{current
frame}.  Some of the debugger commands operate on the current frame.
Debugger commands are mainly used for stepping through code one
expression at a time.  Here is a list of them:

@table @kbd
@item c
Exit the debugger and continue execution.  In most cases, execution of
the program continues as if the debugger had never been entered (aside
from the effect of any variables or data structures you may have changed
while inside the debugger).  This includes entry to the debugger due to
function entry or exit, explicit invocation, and quitting or certain
errors.  Most errors cannot be continued; trying to continue an error usually
causes the same error to occur again.
@item d
Continue execution, but enter the debugger the next time a Lisp
function is called.  This allows you to step through the
subexpressions of an expression, and see what the subexpressions do and
what values they compute.

When you enter the debugger this way, Emacs flags the stack frame for the
function call from which you entered.  The same function is then called
when you exit the frame.  To cancel this flag, use @kbd{u}.
@item b
Set up to enter the debugger when the current frame is exited.  Frames
that invoke the debugger on exit are flagged with stars.
@item u
Don't enter the debugger when the current frame is exited.  This
cancels a @kbd{b} command on a frame.
@item e
Read a Lisp expression in the minibuffer, evaluate it, and print the
value in the echo area.  This is equivalent to the command @kbd{M-:}.
@item q
Terminate the program being debugged; return to top-level Emacs
command execution.

If the debugger was entered due to a @kbd{C-g} but you really want
to quit, not to debug, use the @kbd{q} command.
@item r
Return a value from the debugger.  The value is computed by reading an
expression with the minibuffer and evaluating it.

The value returned by the debugger makes a difference when the debugger
was invoked due to exit from a Lisp call frame (as requested with @kbd{b});
then the value specified in the @kbd{r} command is used as the value of
that frame.

The debugger's return value also matters with many errors.  For example,
@code{wrong-type-argument} errors will use the debugger's return value
instead of the invalid argument; @code{no-catch} errors will use the
debugger value as a throw tag instead of the tag that was not found.
If an error was signaled by calling the Lisp function @code{signal},
the debugger's return value is returned as the value of @code{signal}.
@end table

@node Lisp Interaction, External Lisp, Lisp Debug, Running
@section Lisp Interaction Buffers

  The buffer @samp{*scratch*}, which is selected when Emacs starts up, is
provided for evaluating Lisp expressions interactively inside Emacs.  Both
the expressions you evaluate and their output goes in the buffer.

  The @samp{*scratch*} buffer's major mode is Lisp Interaction mode, which
is the same as Emacs-Lisp mode except for one command, @key{LFD}.  In
Emacs-Lisp mode, @key{LFD} is an indentation command.  In Lisp
Interaction mode, @key{LFD} is bound to @code{eval-print-last-sexp}.  This
function reads the Lisp expression before point, evaluates it, and inserts
the value in printed representation before point.

 The way to use the @samp{*scratch*} buffer is to insert Lisp
expressions at the end, ending each one with @key{LFD} so that it will
be evaluated.  The result is a complete typescript of the expressions
you have evaluated and their values.

@findex lisp-interaction-mode
  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.  @kbd{M-x lisp-interaction-mode} will put any buffer in Lisp
Interaction mode.

@node External Lisp,, Lisp Interaction, Running
@section Running an External Lisp

  Emacs has facilities for running programs in other Lisp systems.  You can
run a Lisp process as an inferior of Emacs, and pass expressions to it to
be evaluated.  You can also pass changed function definitions directly from
the Emacs buffers in which you edit the Lisp programs to the inferior Lisp
process.

@findex run-lisp
  To run an inferior Lisp process, type @kbd{M-x run-lisp}.  This runs the
program named @code{lisp}, the same program you would run by typing
@code{lisp} as a shell command, with both input and output going through an
Emacs buffer named @samp{*lisp*}.  In other words, any ``terminal output''
from Lisp will go into the buffer, advancing point, and any ``terminal
input'' for Lisp comes from text in the buffer.  To give input to Lisp, go
to the end of the buffer and type the input, terminated by @key{RET}.  The
@samp{*lisp*} buffer is in Inferior Lisp mode, which has all the
special characteristics of Lisp mode and Shell mode (@pxref{Shell Mode}).

@findex lisp-mode
  Use Lisp mode to run the source files of programs in external Lisps.
You can select this mode with @kbd{M-x lisp-mode}.  It is used automatically
for files whose names end in @file{.l} or @file{.lisp}, as most Lisp
systems usually expect.

@kindex C-M-x
@findex lisp-send-defun
  When you edit a function in a Lisp program you are running, the easiest
way to send the changed definition to the inferior Lisp process is the key
@kbd{C-M-x}.  In Lisp mode, this key runs the function @code{lisp-send-defun},
which finds the defun around or following point and sends it as input to
the Lisp process.  (Emacs can send input to any inferior process regardless
of what buffer is current.)

  Contrast the meanings of @kbd{C-M-x} in Lisp mode (for editing programs
to be run in another Lisp system) and Emacs-Lisp mode (for editing Lisp
programs to be run in Emacs): in both modes it has the effect of installing
the function definition that point is in, but the way of doing so is
different according to where the relevant Lisp environment is found.
@xref{Lisp Modes}.

repo_name: mthl/texinfo

license: mit