-;;; New backquote for GNU Emacs.
-;;; Copyright (C) 1990, 1992, 1994 Free Software Foundation, Inc.
+;;; backquote.el --- implement the ` Lisp construct
+
+;; Copyright (C) 1990, 1992, 1994, 2001, 2002, 2003, 2004,
+;; 2005, 2006 Free Software Foundation, Inc.
;; Author: Rick Sladkey <jrs@world.std.com>
;; Maintainer: FSF
;; Keywords: extensions, internal
-;; This file is not part of GNU Emacs but is distributed under
-;; the same conditions as GNU Emacs.
+;; This file is part of GNU Emacs.
;; 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 1, or (at your option)
+;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.
;; GNU Emacs is distributed in the hope that it will be useful,
;; 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, 675 Mass Ave, Cambridge, MA 02139, USA.
-
-;; This is a new backquote for GNU Emacs written by
-;; Rick Sladkey <jrs@world.std.com>. It has the following
-;; features compared to the version 18 backquote:
-
-;; Correctly handles nested backquotes.
-;; Correctly handles constants after a splice.
-;; Correctly handles top-level atoms and unquotes.
-;; Correctly handles unquote after dot.
-;; Understands vectors.
-;; Minimizes gratuitous consing.
-;; Faster operation with simpler semantics.
-;; Generates faster run-time expressions.
-;; One third fewer calories than our regular beer.
+;; 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.
+
+;;; Commentary:
+
+;; When the Lisp reader sees `(...), it generates (\` (...)).
+;; When it sees ,... inside such a backquote form, it generates (\, ...).
+;; For ,@... it generates (\,@ ...).
;; This backquote will generate calls to the backquote-list* form.
;; Both a function version and a macro version are included.
"Like `list' but the last argument is the tail of the new list.
For example (backquote-list* 'a 'b 'c) => (a b . c)"
+ ;; The recursive solution is much nicer:
+ ;; (if list (cons first (apply 'backquote-list*-function list)) first))
+ ;; but Emacs is not very good at efficiently processing recursion.
(if list
(let* ((rest list) (newlist (cons first nil)) (last newlist))
(while (cdr rest)
"Like `list' but the last argument is the tail of the new list.
For example (backquote-list* 'a 'b 'c) => (a b . c)"
- (setq list (reverse (cons first list))
+ ;; The recursive solution is much nicer:
+ ;; (if list (list 'cons first (cons 'backquote-list*-macro list)) first))
+ ;; but Emacs is not very good at efficiently processing such things.
+ (setq list (nreverse (cons first list))
first (car list)
list (cdr list))
(if list
newlist)
first))
-(fset 'backquote-list* (symbol-function 'backquote-list*-macro))
+(defalias 'backquote-list* (symbol-function 'backquote-list*-macro))
;; A few advertised variables that control which symbols are used
;; to represent the backquote, unquote, and splice operations.
+(defconst backquote-backquote-symbol '\`
+ "Symbol used to represent a backquote or nested backquote.")
-;;;###autoload
-(defvar backquote-backquote-symbol '`
- "*Symbol used to represent a backquote or nested backquote (e.g. `).")
-
-(defvar backquote-unquote-symbol ',
- "*Symbol used to represent an unquote (e.g. `,') inside a backquote.")
+(defconst backquote-unquote-symbol ',
+ "Symbol used to represent an unquote inside a backquote.")
-(defvar backquote-splice-symbol ',@
- "*Symbol used to represent a splice (e.g. `,'@) inside a backquote.")
+(defconst backquote-splice-symbol ',@
+ "Symbol used to represent a splice inside a backquote.")
;;;###autoload
(defmacro backquote (arg)
For example:
-b => (ba bb bc) ; assume b has this value
-\(` (a b c)) => (a b c) ; backquote acts like quote
-\(` (a (, b) c)) => (a (ba bb bc) c) ; insert the value of b
-\(` (a (,@ b) c)) => (a ba bb bc c) ; splice in the value of b
+b => (ba bb bc) ; assume b has this value
+`(a b c) => (a b c) ; backquote acts like quote
+`(a ,b c) => (a (ba bb bc) c) ; insert the value of b
+`(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)))
;; GNU Emacs has no reader macros
;;;###autoload
-(fset backquote-backquote-symbol (symbol-function 'backquote))
+(defalias '\` (symbol-function 'backquote))
;; backquote-process returns a dotted-pair of a tag (0, 1, or 2) and
;; the backquote-processed structure. 0 => the structure is
(if (= (car n) 0)
(cons 0 s)
(cons 1 (cond
+ ((not (listp (cdr n)))
+ (list 'vconcat (cdr n)))
((eq (nth 1 n) 'list)
(cons 'vector (nthcdr 2 n)))
((eq (nth 1 n) 'append)
;; Scan this list-level, setting LISTS to a list of forms,
;; each of which produces a list of elements
;; that should go in this level.
- ;; The order of LISTS is backwards.
+ ;; The order of LISTS is backwards.
;; If there are non-splicing elements (constant or variable)
;; at the beginning, put them in FIRSTLIST,
;; as a list of tagged values (TAG . FORM).
(setq item (backquote-process (car rest)))
(cond
((= (car item) 2)
- (if (null firstlist)
+ ;; Put the nonspliced items before the first spliced item
+ ;; into FIRSTLIST.
+ (if (null lists)
(setq firstlist list
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))
(if (or rest list)
(setq lists (cons (backquote-listify list (backquote-process rest))
lists)))
- ;; Turn LISTS into a form that produces the combined list.
+ ;; Turn LISTS into a form that produces the combined list.
(setq expression
(if (or (cdr lists)
(eq (car-safe (car lists)) backquote-splice-symbol))
tail))
(t (cons 'list heads)))))
-;; backquote.el ends here
+;;; arch-tag: 1a26206a-6b5e-4c56-8e24-2eef0f7e0e7a
+;;; backquote.el ends here