@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990-1995, 1998, 2001-2012 Free Software Foundation, Inc.
+@c Copyright (C) 1990-1995, 1998, 2001-2012 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../../info/macros
@node Macros, Customization, Functions, Top
definitions that shadow the currently defined macros. Byte compilation
uses this feature.
-@smallexample
+@example
@group
(defmacro inc (var)
(list 'setq var (list '1+ var)))
(macroexpand '(inc2 r s))
@result{} (progn (inc r) (inc s)) ; @r{@code{inc} not expanded here.}
@end group
-@end smallexample
+@end example
@end defun
@code{macroexpand-all}, we see that @code{macroexpand-all} @emph{does}
expand the embedded calls to @code{inc}:
-@smallexample
+@example
(macroexpand-all '(inc2 r s))
@result{} (progn (setq r (1+ r)) (setq s (1+ s)))
-@end smallexample
+@end example
@end defun
problem. This macro allows us to write a ``for'' loop construct.
@findex for
-@smallexample
+@example
@group
(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)))))))
+ (cons 'while
+ (cons (list '<= var final)
+ (append body (list (list 'inc var)))))))
@end group
@result{} for
@print{}3 9
@result{} nil
@end group
-@end smallexample
+@end example
@noindent
The arguments @code{from}, @code{to}, and @code{do} in this macro are
Here's an equivalent definition simplified through use of backquote:
-@smallexample
+@example
@group
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop.
,@@body
(inc ,var))))
@end group
-@end smallexample
+@end example
Both forms of this definition (with backquote and without) suffer from
the defect that @var{final} is evaluated on every iteration. If
once unless repeated evaluation is part of the intended purpose of the
macro. Here is a correct expansion for the @code{for} macro:
-@smallexample
+@example
@group
(let ((i 1)
(max 3))
(princ (format "%d %d" i square))
(inc i)))
@end group
-@end smallexample
+@end example
Here is a macro definition that creates this expansion:
-@smallexample
+@example
@group
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
,@@body
(inc ,var))))
@end group
-@end smallexample
+@end example
Unfortunately, this fix introduces another problem,
described in the following section.
follows to make the expansion evaluate the macro arguments the proper
number of times:
-@smallexample
+@example
@group
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
,@@body
(inc ,var))))
@end group
-@end smallexample
+@end example
@end 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:
-@smallexample
+@example
@group
(let ((max 0))
(for x from 0 to 10 do
(if (< max this)
(setq max this)))))
@end group
-@end smallexample
+@end example
@noindent
The references to @code{max} inside the body of the @code{for}, which
where put by @code{for}. Here is a definition of @code{for} that works
this way:
-@smallexample
+@example
@group
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
,@@body
(inc ,var)))))
@end group
-@end smallexample
+@end example
@noindent
This creates an uninterned symbol named @code{max} and puts it in the
@section Indenting Macros
Within a macro definition, you can use the @code{declare} form
-(@pxref{Defining Macros}) to specify how to @key{TAB} should indent
+(@pxref{Defining Macros}) to specify how @key{TAB} should indent
calls to the macro. An indentation specification is written like this:
@example
HCoop / bpt / emacs.git / blobdiff