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41ea659a | 1 | ;;; New backquote for GNU Emacs. |
d733c5ec | 2 | ;;; Copyright (C) 1990, 1992, 1994 Free Software Foundation, Inc. |
c0274f38 | 3 | |
41ea659a RS |
4 | ;; Author: Rick Sladkey <jrs@world.std.com> |
5 | ;; Maintainer: FSF | |
6 | ;; Keywords: extensions, internal | |
9750e079 | 7 | |
41ea659a RS |
8 | ;; This file is not part of GNU Emacs but is distributed under |
9 | ;; the same conditions as GNU Emacs. | |
c440e42b RS |
10 | |
11 | ;; GNU Emacs is free software; you can redistribute it and/or modify | |
12 | ;; it under the terms of the GNU General Public License as published by | |
41ea659a | 13 | ;; the Free Software Foundation; either version 1, or (at your option) |
c440e42b RS |
14 | ;; any later version. |
15 | ||
16 | ;; GNU Emacs is distributed in the hope that it will be useful, | |
17 | ;; but WITHOUT ANY WARRANTY; without even the implied warranty of | |
18 | ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
19 | ;; GNU General Public License for more details. | |
20 | ||
21 | ;; You should have received a copy of the GNU General Public License | |
22 | ;; along with GNU Emacs; see the file COPYING. If not, write to | |
23 | ;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. | |
24 | ||
41ea659a RS |
25 | ;; This is a new backquote for GNU Emacs written by |
26 | ;; Rick Sladkey <jrs@world.std.com>. It has the following | |
27 | ;; features compared to the version 18 backquote: | |
28 | ||
29 | ;; Correctly handles nested backquotes. | |
30 | ;; Correctly handles constants after a splice. | |
31 | ;; Correctly handles top-level atoms and unquotes. | |
32 | ;; Correctly handles unquote after dot. | |
33 | ;; Understands vectors. | |
34 | ;; Minimizes gratuitous consing. | |
35 | ;; Faster operation with simpler semantics. | |
36 | ;; Generates faster run-time expressions. | |
37 | ;; One third fewer calories than our regular beer. | |
38 | ||
288f95bd | 39 | ;; This backquote will generate calls to the backquote-list* form. |
41ea659a RS |
40 | ;; Both a function version and a macro version are included. |
41 | ;; The macro version is used by default because it is faster | |
42 | ;; and needs no run-time support. It should really be a subr. | |
c440e42b | 43 | |
e5167999 | 44 | ;;; Code: |
c440e42b | 45 | |
49116ac0 JB |
46 | (provide 'backquote) |
47 | ||
288f95bd | 48 | ;; function and macro versions of backquote-list* |
41ea659a | 49 | |
288f95bd | 50 | (defun backquote-list*-function (first &rest list) |
41ea659a RS |
51 | "Like `list' but the last argument is the tail of the new list. |
52 | ||
288f95bd | 53 | For example (backquote-list* 'a 'b 'c) => (a b . c)" |
41ea659a RS |
54 | (if list |
55 | (let* ((rest list) (newlist (cons first nil)) (last newlist)) | |
56 | (while (cdr rest) | |
57 | (setcdr last (cons (car rest) nil)) | |
58 | (setq last (cdr last) | |
59 | rest (cdr rest))) | |
60 | (setcdr last (car rest)) | |
61 | newlist) | |
62 | first)) | |
63 | ||
288f95bd RS |
64 | (defmacro backquote-list*-macro (first &rest list) |
65 | "Like `list' but the last argument is the tail of the new list. | |
41ea659a | 66 | |
288f95bd | 67 | For example (backquote-list* 'a 'b 'c) => (a b . c)" |
41ea659a RS |
68 | (setq list (reverse (cons first list)) |
69 | first (car list) | |
70 | list (cdr list)) | |
71 | (if list | |
72 | (let* ((second (car list)) | |
73 | (rest (cdr list)) | |
74 | (newlist (list 'cons second first))) | |
75 | (while rest | |
76 | (setq newlist (list 'cons (car rest) newlist) | |
77 | rest (cdr rest))) | |
78 | newlist) | |
79 | first)) | |
80 | ||
c9c7f2c4 | 81 | (defalias 'backquote-list* (symbol-function 'backquote-list*-macro)) |
41ea659a RS |
82 | |
83 | ;; A few advertised variables that control which symbols are used | |
84 | ;; to represent the backquote, unquote, and splice operations. | |
85 | ||
86 | (defvar backquote-backquote-symbol '` | |
87 | "*Symbol used to represent a backquote or nested backquote (e.g. `).") | |
88 | ||
89 | (defvar backquote-unquote-symbol ', | |
288f95bd | 90 | "*Symbol used to represent an unquote (e.g. `,') inside a backquote.") |
41ea659a RS |
91 | |
92 | (defvar backquote-splice-symbol ',@ | |
44c48a83 | 93 | "*Symbol used to represent a splice (e.g. `,@') inside a backquote.") |
41ea659a | 94 | |
325e3af2 | 95 | ;;;###autoload |
41ea659a RS |
96 | (defmacro backquote (arg) |
97 | "Argument STRUCTURE describes a template to build. | |
98 | ||
99 | The whole structure acts as if it were quoted except for certain | |
100 | places where expressions are evaluated and inserted or spliced in. | |
101 | ||
102 | For example: | |
103 | ||
104 | b => (ba bb bc) ; assume b has this value | |
105 | \(` (a b c)) => (a b c) ; backquote acts like quote | |
106 | \(` (a (, b) c)) => (a (ba bb bc) c) ; insert the value of b | |
107 | \(` (a (,@ b) c)) => (a ba bb bc c) ; splice in the value of b | |
108 | ||
288f95bd RS |
109 | Vectors work just like lists. Nested backquotes are permitted." |
110 | (cdr (backquote-process arg))) | |
41ea659a RS |
111 | |
112 | ;; GNU Emacs has no reader macros | |
113 | ||
325e3af2 | 114 | ;;;###autoload |
c9c7f2c4 | 115 | (defalias '` (symbol-function 'backquote)) |
41ea659a | 116 | |
288f95bd | 117 | ;; backquote-process returns a dotted-pair of a tag (0, 1, or 2) and |
41ea659a RS |
118 | ;; the backquote-processed structure. 0 => the structure is |
119 | ;; constant, 1 => to be unquoted, 2 => to be spliced in. | |
120 | ;; The top-level backquote macro just discards the tag. | |
121 | ||
288f95bd | 122 | (defun backquote-process (s) |
41ea659a RS |
123 | (cond |
124 | ((vectorp s) | |
288f95bd | 125 | (let ((n (backquote-process (append s ())))) |
41ea659a RS |
126 | (if (= (car n) 0) |
127 | (cons 0 s) | |
128 | (cons 1 (cond | |
129 | ((eq (nth 1 n) 'list) | |
130 | (cons 'vector (nthcdr 2 n))) | |
131 | ((eq (nth 1 n) 'append) | |
132 | (cons 'vconcat (nthcdr 2 n))) | |
133 | (t | |
134 | (list 'apply '(function vector) (cdr n)))))))) | |
135 | ((atom s) | |
136 | (cons 0 (if (or (null s) (eq s t) (not (symbolp s))) | |
137 | s | |
138 | (list 'quote s)))) | |
139 | ((eq (car s) backquote-unquote-symbol) | |
140 | (cons 1 (nth 1 s))) | |
141 | ((eq (car s) backquote-splice-symbol) | |
142 | (cons 2 (nth 1 s))) | |
143 | ((eq (car s) backquote-backquote-symbol) | |
288f95bd | 144 | (backquote-process (cdr (backquote-process (nth 1 s))))) |
41ea659a | 145 | (t |
cd320f32 RS |
146 | (let ((rest s) |
147 | item firstlist list lists expression) | |
148 | ;; Scan this list-level, setting LISTS to a list of forms, | |
149 | ;; each of which produces a list of elements | |
150 | ;; that should go in this level. | |
151 | ;; The order of LISTS is backwards. | |
152 | ;; If there are non-splicing elements (constant or variable) | |
153 | ;; at the beginning, put them in FIRSTLIST, | |
154 | ;; as a list of tagged values (TAG . FORM). | |
155 | ;; If there are any at the end, they go in LIST, likewise. | |
41ea659a | 156 | (while (consp rest) |
cd320f32 | 157 | ;; Turn . (, foo) into (,@ foo). |
41ea659a RS |
158 | (if (eq (car rest) backquote-unquote-symbol) |
159 | (setq rest (list (list backquote-splice-symbol (nth 1 rest))))) | |
288f95bd | 160 | (setq item (backquote-process (car rest))) |
41ea659a RS |
161 | (cond |
162 | ((= (car item) 2) | |
1d08cb50 RS |
163 | ;; Put the nonspliced items before the first spliced item |
164 | ;; into FIRSTLIST. | |
165 | (if (null lists) | |
41ea659a RS |
166 | (setq firstlist list |
167 | list nil)) | |
1d08cb50 | 168 | ;; Otherwise, put any preceding nonspliced items into LISTS. |
41ea659a | 169 | (if list |
288f95bd | 170 | (setq lists (cons (backquote-listify list '(0 . nil)) lists))) |
41ea659a RS |
171 | (setq lists (cons (cdr item) lists)) |
172 | (setq list nil)) | |
173 | (t | |
174 | (setq list (cons item list)))) | |
175 | (setq rest (cdr rest))) | |
cd320f32 RS |
176 | ;; Handle nonsplicing final elements, and the tail of the list |
177 | ;; (which remains in REST). | |
41ea659a | 178 | (if (or rest list) |
288f95bd RS |
179 | (setq lists (cons (backquote-listify list (backquote-process rest)) |
180 | lists))) | |
cd320f32 RS |
181 | ;; Turn LISTS into a form that produces the combined list. |
182 | (setq expression | |
41ea659a | 183 | (if (or (cdr lists) |
cd320f32 | 184 | (eq (car-safe (car lists)) backquote-splice-symbol)) |
41ea659a RS |
185 | (cons 'append (nreverse lists)) |
186 | (car lists))) | |
cd320f32 | 187 | ;; Tack on any initial elements. |
41ea659a | 188 | (if firstlist |
cd320f32 RS |
189 | (setq expression (backquote-listify firstlist (cons 1 expression)))) |
190 | (if (eq (car-safe expression) 'quote) | |
41ea659a | 191 | (cons 0 (list 'quote s)) |
cd320f32 | 192 | (cons 1 expression)))))) |
41ea659a | 193 | |
288f95bd RS |
194 | ;; backquote-listify takes (tag . structure) pairs from backquote-process |
195 | ;; and decides between append, list, backquote-list*, and cons depending | |
41ea659a RS |
196 | ;; on which tags are in the list. |
197 | ||
288f95bd | 198 | (defun backquote-listify (list old-tail) |
41ea659a RS |
199 | (let ((heads nil) (tail (cdr old-tail)) (list-tail list) (item nil)) |
200 | (if (= (car old-tail) 0) | |
201 | (setq tail (eval tail) | |
202 | old-tail nil)) | |
203 | (while (consp list-tail) | |
204 | (setq item (car list-tail)) | |
205 | (setq list-tail (cdr list-tail)) | |
206 | (if (or heads old-tail (/= (car item) 0)) | |
207 | (setq heads (cons (cdr item) heads)) | |
208 | (setq tail (cons (eval (cdr item)) tail)))) | |
209 | (cond | |
210 | (tail | |
211 | (if (null old-tail) | |
212 | (setq tail (list 'quote tail))) | |
213 | (if heads | |
214 | (let ((use-list* (or (cdr heads) | |
215 | (and (consp (car heads)) | |
216 | (eq (car (car heads)) | |
217 | backquote-splice-symbol))))) | |
288f95bd | 218 | (cons (if use-list* 'backquote-list* 'cons) |
41ea659a RS |
219 | (append heads (list tail)))) |
220 | tail)) | |
221 | (t (cons 'list heads))))) | |
222 | ||
223 | ;; backquote.el ends here |