[Emacs-diffs] Changes to macros.texi

[Glenn Morris]

CVSROOT:        /sources/emacs
Module name:    emacs
Changes by:     Glenn Morris <gm>       07/09/06 04:12:40

Index: macros.texi
===================================================================
RCS file: macros.texi
diff -N macros.texi
--- macros.texi 27 Aug 2007 04:00:08 -0000      1.26
+++ /dev/null   1 Jan 1970 00:00:00 -0000
@@ -1,752 +0,0 @@
address@hidden -*-texinfo-*-
address@hidden This is part of the GNU Emacs Lisp Reference Manual.
address@hidden Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 2001, 
2002,
address@hidden   2003, 2004, 2005, 2006, 2007  Free Software Foundation, Inc.
address@hidden See the file elisp.texi for copying conditions.
address@hidden ../info/macros
address@hidden Macros, Customization, Functions, Top
address@hidden Macros
address@hidden macros
-
-  @dfn{Macros} enable you to define new control constructs and other
-language features.  A macro is defined much like a function, but instead
-of telling how to compute a value, it tells how to compute another Lisp
-expression which will in turn compute the value.  We call this
-expression the @dfn{expansion} of the macro.
-
-  Macros can do this because they operate on the unevaluated expressions
-for the arguments, not on the argument values as functions do.  They can
-therefore construct an expansion containing these argument expressions
-or parts of them.
-
-  If you are using a macro to do something an ordinary function could
-do, just for the sake of speed, consider using an inline function
-instead.  @xref{Inline Functions}.
-
address@hidden
-* Simple Macro::            A basic example.
-* Expansion::               How, when and why macros are expanded.
-* Compiling Macros::        How macros are expanded by the compiler.
-* Defining Macros::         How to write a macro definition.
-* Backquote::               Easier construction of list structure.
-* Problems with Macros::    Don't evaluate the macro arguments too many times.
-                              Don't hide the user's variables.
-* Indenting Macros::        Specifying how to indent macro calls.
address@hidden menu
-
address@hidden Simple Macro
address@hidden A Simple Example of a Macro
-
-  Suppose we would like to define a Lisp construct to increment a
-variable value, much like the @code{++} operator in C.  We would like to
-write @code{(inc x)} and have the effect of @code{(setq x (1+ x))}.
-Here's a macro definition that does the job:
-
address@hidden inc
address@hidden
address@hidden
-(defmacro inc (var)
-   (list 'setq var (list '1+ var)))
address@hidden group
address@hidden example
-
-  When this is called with @code{(inc x)}, the argument @var{var} is the
-symbol @address@hidden the @emph{value} of @code{x}, as it would
-be in a function.  The body of the macro uses this to construct the
-expansion, which is @code{(setq x (1+ x))}.  Once the macro definition
-returns this expansion, Lisp proceeds to evaluate it, thus incrementing
address@hidden
-
address@hidden Expansion
address@hidden Expansion of a Macro Call
address@hidden expansion of macros
address@hidden macro call
-
-  A macro call looks just like a function call in that it is a list which
-starts with the name of the macro.  The rest of the elements of the list
-are the arguments of the macro.
-
-  Evaluation of the macro call begins like evaluation of a function call
-except for one crucial difference: the macro arguments are the actual
-expressions appearing in the macro call.  They are not evaluated before
-they are given to the macro definition.  By contrast, the arguments of a
-function are results of evaluating the elements of the function call
-list.
-
-  Having obtained the arguments, Lisp invokes the macro definition just
-as a function is invoked.  The argument variables of the macro are bound
-to the argument values from the macro call, or to a list of them in the
-case of a @code{&rest} argument.  And the macro body executes and
-returns its value just as a function body does.
-
-  The second crucial difference between macros and functions is that the
-value returned by the macro body is not the value of the macro call.
-Instead, it is an alternate expression for computing that value, also
-known as the @dfn{expansion} of the macro.  The Lisp interpreter
-proceeds to evaluate the expansion as soon as it comes back from the
-macro.
-
-  Since the expansion is evaluated in the normal manner, it may contain
-calls to other macros.  It may even be a call to the same macro, though
-this is unusual.
-
-  You can see the expansion of a given macro call by calling
address@hidden
-
address@hidden macroexpand form &optional environment
address@hidden macro expansion
-This function expands @var{form}, if it is a macro call.  If the result
-is another macro call, it is expanded in turn, until something which is
-not a macro call results.  That is the value returned by
address@hidden  If @var{form} is not a macro call to begin with, it
-is returned as given.
-
-Note that @code{macroexpand} does not look at the subexpressions of
address@hidden (although some macro definitions may do so).  Even if they
-are macro calls themselves, @code{macroexpand} does not expand them.
-
-The function @code{macroexpand} does not expand calls to inline functions.
-Normally there is no need for that, since a call to an inline function is
-no harder to understand than a call to an ordinary function.
-
-If @var{environment} is provided, it specifies an alist of macro
-definitions that shadow the currently defined macros.  Byte compilation
-uses this feature.
-
address@hidden
address@hidden
-(defmacro inc (var)
-    (list 'setq var (list '1+ var)))
-     @result{} inc
address@hidden group
-
address@hidden
-(macroexpand '(inc r))
-     @result{} (setq r (1+ r))
address@hidden group
-
address@hidden
-(defmacro inc2 (var1 var2)
-    (list 'progn (list 'inc var1) (list 'inc var2)))
-     @result{} inc2
address@hidden group
-
address@hidden
-(macroexpand '(inc2 r s))
-     @result{} (progn (inc r) (inc s))  ; @address@hidden not expanded here.}
address@hidden group
address@hidden smallexample
address@hidden defun
-
-
address@hidden macroexpand-all form &optional environment
address@hidden expands macros like @code{macroexpand}, but
-will look for and expand all macros in @var{form}, not just at the
-top-level.  If no macros are expanded, the return value is @code{eq}
-to @var{form}.
-
-Repeating the example used for @code{macroexpand} above with
address@hidden, we see that @code{macroexpand-all} @emph{does}
-expand the embedded calls to @code{inc}:
-
address@hidden
-(macroexpand-all '(inc2 r s))
-     @result{} (progn (setq r (1+ r)) (setq s (1+ s)))
address@hidden smallexample
-
address@hidden defun
-
address@hidden Compiling Macros
address@hidden Macros and Byte Compilation
address@hidden byte-compiling macros
-
-  You might ask why we take the trouble to compute an expansion for a
-macro and then evaluate the expansion.  Why not have the macro body
-produce the desired results directly?  The reason has to do with
-compilation.
-
-  When a macro call appears in a Lisp program being compiled, the Lisp
-compiler calls the macro definition just as the interpreter would, and
-receives an expansion.  But instead of evaluating this expansion, it
-compiles the expansion as if it had appeared directly in the program.
-As a result, the compiled code produces the value and side effects
-intended for the macro, but executes at full compiled speed.  This would
-not work if the macro body computed the value and side effects
-itself---they would be computed at compile time, which is not useful.
-
-  In order for compilation of macro calls to work, the macros must
-already be defined in Lisp when the calls to them are compiled.  The
-compiler has a special feature to help you do this: if a file being
-compiled contains a @code{defmacro} form, the macro is defined
-temporarily for the rest of the compilation of that file.  To make this
-feature work, you must put the @code{defmacro} in the same file where it
-is used, and before its first use.
-
-  Byte-compiling a file executes any @code{require} calls at top-level
-in the file.  This is in case the file needs the required packages for
-proper compilation.  One way to ensure that necessary macro definitions
-are available during compilation is to require the files that define
-them (@pxref{Named Features}).  To avoid loading the macro definition files
-when someone @emph{runs} the compiled program, write
address@hidden around the @code{require} calls (@pxref{Eval
-During Compile}).
-
address@hidden Defining Macros
address@hidden Defining Macros
-
-  A Lisp macro is a list whose @sc{car} is @code{macro}.  Its @sc{cdr} should
-be a function; expansion of the macro works by applying the function
-(with @code{apply}) to the list of unevaluated argument-expressions
-from the macro call.
-
-  It is possible to use an anonymous Lisp macro just like an anonymous
-function, but this is never done, because it does not make sense to pass
-an anonymous macro to functionals such as @code{mapcar}.  In practice,
-all Lisp macros have names, and they are usually defined with the
-special form @code{defmacro}.
-
address@hidden defmacro name argument-list address@hidden
address@hidden defines the symbol @var{name} as a macro that looks
-like this:
-
address@hidden
-(macro lambda @var{argument-list} . @var{body-forms})
address@hidden example
-
-(Note that the @sc{cdr} of this list is a function---a lambda expression.)
-This macro object is stored in the function cell of @var{name}.  The
-value returned by evaluating the @code{defmacro} form is @var{name}, but
-usually we ignore this value.
-
-The shape and meaning of @var{argument-list} is the same as in a
-function, and the keywords @code{&rest} and @code{&optional} may be used
-(@pxref{Argument List}).  Macros may have a documentation string, but
-any @code{interactive} declaration is ignored since macros cannot be
-called interactively.
address@hidden defspec
-
-  The body of the macro definition can include a @code{declare} form,
-which can specify how @key{TAB} should indent macro calls, and how to
-step through them for Edebug.
-
address@hidden declare @address@hidden
address@hidden of declare}
-A @code{declare} form is used in a macro definition to specify various
-additional information about it.  Two kinds of specification are
-currently supported:
-
address@hidden @code
address@hidden (debug @var{edebug-form-spec})
-Specify how to step through macro calls for Edebug.
address@hidden Macro Calls}.
-
address@hidden (indent @var{indent-spec})
-Specify how to indent calls to this macro.  @xref{Indenting Macros},
-for more details.
address@hidden table
-
-A @code{declare} form only has its special effect in the body of a
address@hidden form if it immediately follows the documentation
-string, if present, or the argument list otherwise.  (Strictly
-speaking, @emph{several} @code{declare} forms can follow the
-documentation string or argument list, but since a @code{declare} form
-can have several @var{specs}, they can always be combined into a
-single form.)  When used at other places in a @code{defmacro} form, or
-outside a @code{defmacro} form, @code{declare} just returns @code{nil}
-without evaluating any @var{specs}.
address@hidden defmac
-
-  No macro absolutely needs a @code{declare} form, because that form
-has no effect on how the macro expands, on what the macro means in the
-program.  It only affects secondary features: indentation and Edebug.
-
address@hidden Backquote
address@hidden Backquote
address@hidden backquote (list substitution)
address@hidden ` (list substitution)
address@hidden `
-
-  Macros often need to construct large list structures from a mixture of
-constants and nonconstant parts.  To make this easier, use the @samp{`}
-syntax (usually called @dfn{backquote}).
-
-  Backquote allows you to quote a list, but selectively evaluate
-elements of that list.  In the simplest case, it is identical to the
-special form @code{quote} (@pxref{Quoting}).  For example, these
-two forms yield identical results:
-
address@hidden
address@hidden
-`(a list of (+ 2 3) elements)
-     @result{} (a list of (+ 2 3) elements)
address@hidden group
address@hidden
-'(a list of (+ 2 3) elements)
-     @result{} (a list of (+ 2 3) elements)
address@hidden group
address@hidden example
-
address@hidden , @r{(with backquote)}
-The special marker @samp{,} inside of the argument to backquote
-indicates a value that isn't constant.  Backquote evaluates the
-argument of @samp{,} and puts the value in the list structure:
-
address@hidden
address@hidden
-(list 'a 'list 'of (+ 2 3) 'elements)
-     @result{} (a list of 5 elements)
address@hidden group
address@hidden
-`(a list of ,(+ 2 3) elements)
-     @result{} (a list of 5 elements)
address@hidden group
address@hidden example
-
-  Substitution with @samp{,} is allowed at deeper levels of the list
-structure also.  For example:
-
address@hidden
address@hidden
-(defmacro t-becomes-nil (variable)
-  `(if (eq ,variable t)
-       (setq ,variable nil)))
address@hidden group
-
address@hidden
-(t-becomes-nil foo)
-     @equiv{} (if (eq foo t) (setq foo nil))
address@hidden group
address@hidden example
-
address@hidden ,@@ @r{(with backquote)}
address@hidden splicing (with backquote)
-  You can also @dfn{splice} an evaluated value into the resulting list,
-using the special marker @samp{,@@}.  The elements of the spliced list
-become elements at the same level as the other elements of the resulting
-list.  The equivalent code without using @samp{`} is often unreadable.
-Here are some examples:
-
address@hidden
address@hidden
-(setq some-list '(2 3))
-     @result{} (2 3)
address@hidden group
address@hidden
-(cons 1 (append some-list '(4) some-list))
-     @result{} (1 2 3 4 2 3)
address@hidden group
address@hidden
-`(1 ,@@some-list 4 ,@@some-list)
-     @result{} (1 2 3 4 2 3)
address@hidden group
-
address@hidden
-(setq list '(hack foo bar))
-     @result{} (hack foo bar)
address@hidden group
address@hidden
-(cons 'use
-  (cons 'the
-    (cons 'words (append (cdr list) '(as elements)))))
-     @result{} (use the words foo bar as elements)
address@hidden group
address@hidden
-`(use the words ,@@(cdr list) as elements)
-     @result{} (use the words foo bar as elements)
address@hidden group
address@hidden example
-
-In old Emacs versions, before version 19.29, @samp{`} used a different
-syntax which required an extra level of parentheses around the entire
-backquote construct.  Likewise, each @samp{,} or @samp{,@@} substitution
-required an extra level of parentheses surrounding both the @samp{,} or
address@hidden,@@} and the following expression.  The old syntax required
-whitespace between the @samp{`}, @samp{,} or @samp{,@@} and the
-following expression.
-
-This syntax is still accepted, for compatibility with old Emacs
-versions, but support for it will soon disappear.
-
address@hidden Problems with Macros
address@hidden Common Problems Using Macros
-
-  The basic facts of macro expansion have counterintuitive consequences.
-This section describes some important consequences that can lead to
-trouble, and rules to follow to avoid trouble.
-
address@hidden
-* Wrong Time::             Do the work in the expansion, not in the macro.
-* Argument Evaluation::    The expansion should evaluate each macro arg once.
-* Surprising Local Vars::  Local variable bindings in the expansion
-                              require special care.
-* Eval During Expansion::  Don't evaluate them; put them in the expansion.
-* Repeated Expansion::     Avoid depending on how many times expansion is done.
address@hidden menu
-
address@hidden Wrong Time
address@hidden Wrong Time
-
-  The most common problem in writing macros is doing some of the
-real work prematurely---while expanding the macro, rather than in the
-expansion itself.  For instance, one real package had this macro
-definition:
-
address@hidden
-(defmacro my-set-buffer-multibyte (arg)
-  (if (fboundp 'set-buffer-multibyte)
-      (set-buffer-multibyte arg)))
address@hidden example
-
-With this erroneous macro definition, the program worked fine when
-interpreted but failed when compiled.  This macro definition called
address@hidden during compilation, which was wrong, and
-then did nothing when the compiled package was run.  The definition
-that the programmer really wanted was this:
-
address@hidden
-(defmacro my-set-buffer-multibyte (arg)
-  (if (fboundp 'set-buffer-multibyte)
-      `(set-buffer-multibyte ,arg)))
address@hidden example
-
address@hidden
-This macro expands, if appropriate, into a call to
address@hidden that will be executed when the compiled
-program is actually run.
-
address@hidden Argument Evaluation
address@hidden Evaluating Macro Arguments Repeatedly
-
-  When defining a macro you must pay attention to the number of times
-the arguments will be evaluated when the expansion is executed.  The
-following macro (used to facilitate iteration) illustrates the problem.
-This macro allows us to write a simple ``for'' loop such as one might
-find in Pascal.
-
address@hidden for
address@hidden
address@hidden
-(defmacro for (var from init to final do &rest body)
-  "Execute a simple \"for\" loop.
-For example, (for i from 1 to 10 do (print i))."
-  (list 'let (list (list var init))
-        (cons 'while (cons (list '<= var final)
-                           (append body (list (list 'inc var)))))))
address@hidden group
address@hidden for
-
address@hidden
-(for i from 1 to 3 do
-   (setq square (* i i))
-   (princ (format "\n%d %d" i square)))
address@hidden
address@hidden group
address@hidden
-(let ((i 1))
-  (while (<= i 3)
-    (setq square (* i i))
-    (princ (format "\n%d %d" i square))
-    (inc i)))
address@hidden group
address@hidden
-
-     @print{}1       1
-     @print{}2       4
-     @print{}3       9
address@hidden nil
address@hidden group
address@hidden smallexample
-
address@hidden
-The arguments @code{from}, @code{to}, and @code{do} in this macro are
-``syntactic sugar''; they are entirely ignored.  The idea is that you
-will write noise words (such as @code{from}, @code{to}, and @code{do})
-in those positions in the macro call.
-
-Here's an equivalent definition simplified through use of backquote:
-
address@hidden
address@hidden
-(defmacro for (var from init to final do &rest body)
-  "Execute a simple \"for\" loop.
-For example, (for i from 1 to 10 do (print i))."
-  `(let ((,var ,init))
-     (while (<= ,var ,final)
-       ,@@body
-       (inc ,var))))
address@hidden group
address@hidden smallexample
-
-Both forms of this definition (with backquote and without) suffer from
-the defect that @var{final} is evaluated on every iteration.  If
address@hidden is a constant, this is not a problem.  If it is a more
-complex form, say @code{(long-complex-calculation x)}, this can slow
-down the execution significantly.  If @var{final} has side effects,
-executing it more than once is probably incorrect.
-
address@hidden macro argument evaluation
-A well-designed macro definition takes steps to avoid this problem by
-producing an expansion that evaluates the argument expressions exactly
-once unless repeated evaluation is part of the intended purpose of the
-macro.  Here is a correct expansion for the @code{for} macro:
-
address@hidden
address@hidden
-(let ((i 1)
-      (max 3))
-  (while (<= i max)
-    (setq square (* i i))
-    (princ (format "%d      %d" i square))
-    (inc i)))
address@hidden group
address@hidden smallexample
-
-Here is a macro definition that creates this expansion:
-
address@hidden
address@hidden
-(defmacro for (var from init to final do &rest body)
-  "Execute a simple for loop: (for i from 1 to 10 do (print i))."
-  `(let ((,var ,init)
-         (max ,final))
-     (while (<= ,var max)
-       ,@@body
-       (inc ,var))))
address@hidden group
address@hidden smallexample
-
-  Unfortunately, this fix introduces another problem,
-described in the following section.
-
address@hidden Surprising Local Vars
address@hidden Local Variables in Macro Expansions
-
address@hidden
-  In the previous section, the definition of @code{for} was fixed as
-follows to make the expansion evaluate the macro arguments the proper
-number of times:
-
address@hidden
address@hidden
-(defmacro for (var from init to final do &rest body)
-  "Execute a simple for loop: (for i from 1 to 10 do (print i))."
address@hidden group
address@hidden
-  `(let ((,var ,init)
-         (max ,final))
-     (while (<= ,var max)
-       ,@@body
-       (inc ,var))))
address@hidden group
address@hidden smallexample
address@hidden ifnottex
-
-  The new definition of @code{for} has a new problem: it introduces a
-local variable named @code{max} which the user does not expect.  This
-causes trouble in examples such as the following:
-
address@hidden
address@hidden
-(let ((max 0))
-  (for x from 0 to 10 do
-    (let ((this (frob x)))
-      (if (< max this)
-          (setq max this)))))
address@hidden group
address@hidden smallexample
-
address@hidden
-The references to @code{max} inside the body of the @code{for}, which
-are supposed to refer to the user's binding of @code{max}, really access
-the binding made by @code{for}.
-
-The way to correct this is to use an uninterned symbol instead of
address@hidden (@pxref{Creating Symbols}).  The uninterned symbol can be
-bound and referred to just like any other symbol, but since it is
-created by @code{for}, we know that it cannot already appear in the
-user's program.  Since it is not interned, there is no way the user can
-put it into the program later.  It will never appear anywhere except
-where put by @code{for}.  Here is a definition of @code{for} that works
-this way:
-
address@hidden
address@hidden
-(defmacro for (var from init to final do &rest body)
-  "Execute a simple for loop: (for i from 1 to 10 do (print i))."
-  (let ((tempvar (make-symbol "max")))
-    `(let ((,var ,init)
-           (,tempvar ,final))
-       (while (<= ,var ,tempvar)
-         ,@@body
-         (inc ,var)))))
address@hidden group
address@hidden smallexample
-
address@hidden
-This creates an uninterned symbol named @code{max} and puts it in the
-expansion instead of the usual interned symbol @code{max} that appears
-in expressions ordinarily.
-
address@hidden Eval During Expansion
address@hidden Evaluating Macro Arguments in Expansion
-
-  Another problem can happen if the macro definition itself
-evaluates any of the macro argument expressions, such as by calling
address@hidden (@pxref{Eval}).  If the argument is supposed to refer to the
-user's variables, you may have trouble if the user happens to use a
-variable with the same name as one of the macro arguments.  Inside the
-macro body, the macro argument binding is the most local binding of this
-variable, so any references inside the form being evaluated do refer to
-it.  Here is an example:
-
address@hidden
address@hidden
-(defmacro foo (a)
-  (list 'setq (eval a) t))
-     @result{} foo
address@hidden group
address@hidden
-(setq x 'b)
-(foo x) @expansion{} (setq b t)
-     @result{} t                  ; @r{and @code{b} has been set.}
-;; @r{but}
-(setq a 'c)
-(foo a) @expansion{} (setq a t)
-     @result{} t                  ; @r{but this set @code{a}, not @code{c}.}
-
address@hidden group
address@hidden example
-
-  It makes a difference whether the user's variable is named @code{a} or
address@hidden, because @code{a} conflicts with the macro argument variable
address@hidden
-
-  Another problem with calling @code{eval} in a macro definition is that
-it probably won't do what you intend in a compiled program.  The
-byte-compiler runs macro definitions while compiling the program, when
-the program's own computations (which you might have wished to access
-with @code{eval}) don't occur and its local variable bindings don't
-exist.
-
-  To avoid these problems, @strong{don't evaluate an argument expression
-while computing the macro expansion}.  Instead, substitute the
-expression into the macro expansion, so that its value will be computed
-as part of executing the expansion.  This is how the other examples in
-this chapter work.
-
address@hidden Repeated Expansion
address@hidden How Many Times is the Macro Expanded?
-
-  Occasionally problems result from the fact that a macro call is
-expanded each time it is evaluated in an interpreted function, but is
-expanded only once (during compilation) for a compiled function.  If the
-macro definition has side effects, they will work differently depending
-on how many times the macro is expanded.
-
-  Therefore, you should avoid side effects in computation of the
-macro expansion, unless you really know what you are doing.
-
-  One special kind of side effect can't be avoided: constructing Lisp
-objects.  Almost all macro expansions include constructed lists; that is
-the whole point of most macros.  This is usually safe; there is just one
-case where you must be careful: when the object you construct is part of a
-quoted constant in the macro expansion.
-
-  If the macro is expanded just once, in compilation, then the object is
-constructed just once, during compilation.  But in interpreted
-execution, the macro is expanded each time the macro call runs, and this
-means a new object is constructed each time.
-
-  In most clean Lisp code, this difference won't matter.  It can matter
-only if you perform side-effects on the objects constructed by the macro
-definition.  Thus, to avoid trouble, @strong{avoid side effects on
-objects constructed by macro definitions}.  Here is an example of how
-such side effects can get you into trouble:
-
address@hidden
address@hidden
-(defmacro empty-object ()
-  (list 'quote (cons nil nil)))
address@hidden group
-
address@hidden
-(defun initialize (condition)
-  (let ((object (empty-object)))
-    (if condition
-        (setcar object condition))
-    object))
address@hidden group
address@hidden lisp
-
address@hidden
-If @code{initialize} is interpreted, a new list @code{(nil)} is
-constructed each time @code{initialize} is called.  Thus, no side effect
-survives between calls.  If @code{initialize} is compiled, then the
-macro @code{empty-object} is expanded during compilation, producing a
-single ``constant'' @code{(nil)} that is reused and altered each time
address@hidden is called.
-
-One way to avoid pathological cases like this is to think of
address@hidden as a funny kind of constant, not as a memory
-allocation construct.  You wouldn't use @code{setcar} on a constant such
-as @code{'(nil)}, so naturally you won't use it on @code{(empty-object)}
-either.
-
address@hidden Indenting Macros
address@hidden Indenting Macros
-
-  You can use the @code{declare} form in the macro definition to
-specify how to @key{TAB} should indent indent calls to the macro.  You
-write it like this:
-
address@hidden
-(declare (indent @var{indent-spec}))
address@hidden example
-
address@hidden
-Here are the possibilities for @var{indent-spec}:
-
address@hidden @asis
address@hidden @code{nil}
-This is the same as no property---use the standard indentation pattern.
address@hidden @code{defun}
-Handle this function like a @samp{def} construct: treat the second
-line as the start of a @dfn{body}.
address@hidden an integer, @var{number}
-The first @var{number} arguments of the function are
address@hidden arguments; the rest are considered the body
-of the expression.  A line in the expression is indented according to
-whether the first argument on it is distinguished or not.  If the
-argument is part of the body, the line is indented @code{lisp-body-indent}
-more columns than the open-parenthesis starting the containing
-expression.  If the argument is distinguished and is either the first
-or second argument, it is indented @emph{twice} that many extra columns.
-If the argument is distinguished and not the first or second argument,
-the line uses the standard pattern.
address@hidden a symbol, @var{symbol}
address@hidden should be a function name; that function is called to
-calculate the indentation of a line within this expression.  The
-function receives two arguments:
address@hidden @asis
address@hidden @var{state}
-The value returned by @code{parse-partial-sexp} (a Lisp primitive for
-indentation and nesting computation) when it parses up to the
-beginning of this line.
address@hidden @var{pos}
-The position at which the line being indented begins.
address@hidden table
address@hidden
-It should return either a number, which is the number of columns of
-indentation for that line, or a list whose car is such a number.  The
-difference between returning a number and returning a list is that a
-number says that all following lines at the same nesting level should
-be indented just like this one; a list says that following lines might
-call for different indentations.  This makes a difference when the
-indentation is being computed by @kbd{C-M-q}; if the value is a
-number, @kbd{C-M-q} need not recalculate indentation for the following
-lines until the end of the list.
address@hidden table
-
address@hidden
-   arch-tag: d4cce66d-1047-45c3-bfde-db6719d6e82b
address@hidden ignore