;;; backquote.el --- implement the ` Lisp construct
;; Copyright (C) 1990, 1992, 1994, 2001, 2002, 2003, 2004,
-;; 2005, 2006, 2007 Free Software Foundation, Inc.
+;; 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
;; Author: Rick Sladkey <jrs@world.std.com>
;; Maintainer: FSF
;; This file is part of GNU Emacs.
-;; GNU Emacs is free software; you can redistribute it and/or modify
+;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
-;; the Free Software Foundation; either version 3, or (at your option)
-;; any later version.
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
-;; along with GNU Emacs; see the file COPYING. If not, write to the
-;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
-;; Boston, MA 02110-1301, USA.
+;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
;;; Commentary:
(defconst backquote-backquote-symbol '\`
"Symbol used to represent a backquote or nested backquote.")
-(defconst backquote-unquote-symbol ',
+(defconst backquote-unquote-symbol '\,
"Symbol used to represent an unquote inside a backquote.")
-(defconst backquote-splice-symbol ',@
+(defconst backquote-splice-symbol '\,@
"Symbol used to represent a splice inside a backquote.")
-;;;###autoload
-(defmacro backquote (arg)
+(defmacro backquote (structure)
"Argument STRUCTURE describes a template to build.
The whole structure acts as if it were quoted except for certain
`(a ,@b c) => (a ba bb bc c) ; splice in the value of b
Vectors work just like lists. Nested backquotes are permitted."
- (cdr (backquote-process arg)))
+ (cdr (backquote-process structure)))
;; GNU Emacs has no reader macros
-;;;###autoload
(defalias '\` (symbol-function 'backquote))
;; backquote-process returns a dotted-pair of a tag (0, 1, or 2) and
;; constant, 1 => to be unquoted, 2 => to be spliced in.
;; The top-level backquote macro just discards the tag.
-(defun backquote-process (s)
+(defun backquote-delay-process (s level)
+ "Process a (un|back|splice)quote inside a backquote.
+This simply recurses through the body."
+ (let ((exp (backquote-listify (list (cons 0 (list 'quote (car s))))
+ (backquote-process (cdr s) level))))
+ (if (eq (car-safe exp) 'quote)
+ (cons 0 (list 'quote s))
+ (cons 1 exp))))
+
+(defun backquote-process (s &optional level)
+ "Process the body of a backquote.
+S is the body. Returns a cons cell whose cdr is piece of code which
+is the macro-expansion of S, and whose car is a small integer whose value
+can either indicate that the code is constant (0), or not (1), or returns
+a list which should be spliced into its environment (2).
+LEVEL is only used internally and indicates the nesting level:
+0 (the default) is for the toplevel nested inside a single backquote."
+ (unless level (setq level 0))
(cond
((vectorp s)
- (let ((n (backquote-process (append s ()))))
+ (let ((n (backquote-process (append s ()) level)))
(if (= (car n) 0)
(cons 0 s)
(cons 1 (cond
s
(list 'quote s))))
((eq (car s) backquote-unquote-symbol)
- (cons 1 (nth 1 s)))
+ (if (<= level 0)
+ (cons 1 (nth 1 s))
+ (backquote-delay-process s (1- level))))
((eq (car s) backquote-splice-symbol)
- (cons 2 (nth 1 s)))
+ (if (<= level 0)
+ (cons 2 (nth 1 s))
+ (backquote-delay-process s (1- level))))
((eq (car s) backquote-backquote-symbol)
- (backquote-process (cdr (backquote-process (nth 1 s)))))
+ (backquote-delay-process s (1+ level)))
(t
(let ((rest s)
item firstlist list lists expression)
;; at the beginning, put them in FIRSTLIST,
;; as a list of tagged values (TAG . FORM).
;; If there are any at the end, they go in LIST, likewise.
- (while (consp rest)
- ;; Turn . (, foo) into (,@ foo).
- (if (eq (car rest) backquote-unquote-symbol)
- (setq rest (list (list backquote-splice-symbol (nth 1 rest)))))
- (setq item (backquote-process (car rest)))
+ (while (and (consp rest)
+ ;; Stop if the cdr is an expression inside a backquote or
+ ;; unquote since this needs to go recursively through
+ ;; backquote-process.
+ (not (or (eq (car rest) backquote-unquote-symbol)
+ (eq (car rest) backquote-backquote-symbol))))
+ (setq item (backquote-process (car rest) level))
(cond
((= (car item) 2)
;; Put the nonspliced items before the first spliced item
list nil))
;; Otherwise, put any preceding nonspliced items into LISTS.
(if list
- (setq lists (cons (backquote-listify list '(0 . nil)) lists)))
- (setq lists (cons (cdr item) lists))
+ (push (backquote-listify list '(0 . nil)) lists))
+ (push (cdr item) lists)
(setq list nil))
(t
(setq list (cons item list))))
;; Handle nonsplicing final elements, and the tail of the list
;; (which remains in REST).
(if (or rest list)
- (setq lists (cons (backquote-listify list (backquote-process rest))
- lists)))
+ (push (backquote-listify list (backquote-process rest level))
+ lists))
;; Turn LISTS into a form that produces the combined list.
(setq expression
(if (or (cdr lists)
tail))
(t (cons 'list heads)))))
-;;; arch-tag: 1a26206a-6b5e-4c56-8e24-2eef0f7e0e7a
+;; arch-tag: 1a26206a-6b5e-4c56-8e24-2eef0f7e0e7a
;;; backquote.el ends here
HCoop / bpt / emacs.git / blobdiff