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b035a678 | 1 | ;;; backquote.el --- implement the ` Lisp construct |
b578f267 | 2 | |
d733c5ec | 3 | ;;; Copyright (C) 1990, 1992, 1994 Free Software Foundation, Inc. |
c0274f38 | 4 | |
41ea659a RS |
5 | ;; Author: Rick Sladkey <jrs@world.std.com> |
6 | ;; Maintainer: FSF | |
7 | ;; Keywords: extensions, internal | |
9750e079 | 8 | |
be010748 | 9 | ;; This file is part of 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 | |
7c938215 | 13 | ;; the Free Software Foundation; either version 2, 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 | |
b578f267 EN |
22 | ;; along with GNU Emacs; see the file COPYING. If not, write to the |
23 | ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330, | |
24 | ;; Boston, MA 02111-1307, USA. | |
c440e42b | 25 | |
be010748 | 26 | ;;; Commentary: |
41ea659a | 27 | |
288f95bd | 28 | ;; This backquote will generate calls to the backquote-list* form. |
41ea659a RS |
29 | ;; Both a function version and a macro version are included. |
30 | ;; The macro version is used by default because it is faster | |
31 | ;; and needs no run-time support. It should really be a subr. | |
c440e42b | 32 | |
e5167999 | 33 | ;;; Code: |
c440e42b | 34 | |
49116ac0 JB |
35 | (provide 'backquote) |
36 | ||
288f95bd | 37 | ;; function and macro versions of backquote-list* |
41ea659a | 38 | |
288f95bd | 39 | (defun backquote-list*-function (first &rest list) |
41ea659a RS |
40 | "Like `list' but the last argument is the tail of the new list. |
41 | ||
288f95bd | 42 | For example (backquote-list* 'a 'b 'c) => (a b . c)" |
41ea659a RS |
43 | (if list |
44 | (let* ((rest list) (newlist (cons first nil)) (last newlist)) | |
45 | (while (cdr rest) | |
46 | (setcdr last (cons (car rest) nil)) | |
47 | (setq last (cdr last) | |
48 | rest (cdr rest))) | |
49 | (setcdr last (car rest)) | |
50 | newlist) | |
51 | first)) | |
52 | ||
288f95bd RS |
53 | (defmacro backquote-list*-macro (first &rest list) |
54 | "Like `list' but the last argument is the tail of the new list. | |
41ea659a | 55 | |
288f95bd | 56 | For example (backquote-list* 'a 'b 'c) => (a b . c)" |
41ea659a RS |
57 | (setq list (reverse (cons first list)) |
58 | first (car list) | |
59 | list (cdr list)) | |
60 | (if list | |
61 | (let* ((second (car list)) | |
62 | (rest (cdr list)) | |
63 | (newlist (list 'cons second first))) | |
64 | (while rest | |
65 | (setq newlist (list 'cons (car rest) newlist) | |
66 | rest (cdr rest))) | |
67 | newlist) | |
68 | first)) | |
69 | ||
c9c7f2c4 | 70 | (defalias 'backquote-list* (symbol-function 'backquote-list*-macro)) |
41ea659a RS |
71 | |
72 | ;; A few advertised variables that control which symbols are used | |
73 | ;; to represent the backquote, unquote, and splice operations. | |
4c548238 DL |
74 | (defconst backquote-backquote-symbol '\` |
75 | "*Symbol used to represent a backquote or nested backquote.") | |
76 | ||
77 | (defconst backquote-unquote-symbol ', | |
78 | "*Symbol used to represent an unquote inside a backquote.") | |
79 | ||
80 | (defconst backquote-splice-symbol ',@ | |
81 | "*Symbol used to represent a splice inside a backquote.") | |
41ea659a | 82 | |
325e3af2 | 83 | ;;;###autoload |
41ea659a RS |
84 | (defmacro backquote (arg) |
85 | "Argument STRUCTURE describes a template to build. | |
86 | ||
87 | The whole structure acts as if it were quoted except for certain | |
88 | places where expressions are evaluated and inserted or spliced in. | |
89 | ||
90 | For example: | |
91 | ||
1df90f8f RS |
92 | b => (ba bb bc) ; assume b has this value |
93 | `(a b c) => (a b c) ; backquote acts like quote | |
2b1c5e12 RS |
94 | `(a ,b c) => (a (ba bb bc) c) ; insert the value of b |
95 | `(a ,@b c) => (a ba bb bc c) ; splice in the value of b | |
41ea659a | 96 | |
288f95bd RS |
97 | Vectors work just like lists. Nested backquotes are permitted." |
98 | (cdr (backquote-process arg))) | |
41ea659a RS |
99 | |
100 | ;; GNU Emacs has no reader macros | |
101 | ||
325e3af2 | 102 | ;;;###autoload |
1df90f8f | 103 | (defalias '\` (symbol-function 'backquote)) |
41ea659a | 104 | |
288f95bd | 105 | ;; backquote-process returns a dotted-pair of a tag (0, 1, or 2) and |
41ea659a RS |
106 | ;; the backquote-processed structure. 0 => the structure is |
107 | ;; constant, 1 => to be unquoted, 2 => to be spliced in. | |
108 | ;; The top-level backquote macro just discards the tag. | |
109 | ||
288f95bd | 110 | (defun backquote-process (s) |
41ea659a RS |
111 | (cond |
112 | ((vectorp s) | |
288f95bd | 113 | (let ((n (backquote-process (append s ())))) |
41ea659a RS |
114 | (if (= (car n) 0) |
115 | (cons 0 s) | |
116 | (cons 1 (cond | |
ea4a56de RS |
117 | ((not (listp (cdr n))) |
118 | (list 'vconcat (cdr n))) | |
41ea659a RS |
119 | ((eq (nth 1 n) 'list) |
120 | (cons 'vector (nthcdr 2 n))) | |
121 | ((eq (nth 1 n) 'append) | |
122 | (cons 'vconcat (nthcdr 2 n))) | |
123 | (t | |
124 | (list 'apply '(function vector) (cdr n)))))))) | |
125 | ((atom s) | |
126 | (cons 0 (if (or (null s) (eq s t) (not (symbolp s))) | |
127 | s | |
128 | (list 'quote s)))) | |
129 | ((eq (car s) backquote-unquote-symbol) | |
130 | (cons 1 (nth 1 s))) | |
131 | ((eq (car s) backquote-splice-symbol) | |
132 | (cons 2 (nth 1 s))) | |
133 | ((eq (car s) backquote-backquote-symbol) | |
288f95bd | 134 | (backquote-process (cdr (backquote-process (nth 1 s))))) |
41ea659a | 135 | (t |
cd320f32 RS |
136 | (let ((rest s) |
137 | item firstlist list lists expression) | |
138 | ;; Scan this list-level, setting LISTS to a list of forms, | |
139 | ;; each of which produces a list of elements | |
140 | ;; that should go in this level. | |
141 | ;; The order of LISTS is backwards. | |
142 | ;; If there are non-splicing elements (constant or variable) | |
143 | ;; at the beginning, put them in FIRSTLIST, | |
144 | ;; as a list of tagged values (TAG . FORM). | |
145 | ;; If there are any at the end, they go in LIST, likewise. | |
41ea659a | 146 | (while (consp rest) |
cd320f32 | 147 | ;; Turn . (, foo) into (,@ foo). |
41ea659a RS |
148 | (if (eq (car rest) backquote-unquote-symbol) |
149 | (setq rest (list (list backquote-splice-symbol (nth 1 rest))))) | |
288f95bd | 150 | (setq item (backquote-process (car rest))) |
41ea659a RS |
151 | (cond |
152 | ((= (car item) 2) | |
1d08cb50 RS |
153 | ;; Put the nonspliced items before the first spliced item |
154 | ;; into FIRSTLIST. | |
155 | (if (null lists) | |
41ea659a RS |
156 | (setq firstlist list |
157 | list nil)) | |
1d08cb50 | 158 | ;; Otherwise, put any preceding nonspliced items into LISTS. |
41ea659a | 159 | (if list |
288f95bd | 160 | (setq lists (cons (backquote-listify list '(0 . nil)) lists))) |
41ea659a RS |
161 | (setq lists (cons (cdr item) lists)) |
162 | (setq list nil)) | |
163 | (t | |
164 | (setq list (cons item list)))) | |
165 | (setq rest (cdr rest))) | |
cd320f32 RS |
166 | ;; Handle nonsplicing final elements, and the tail of the list |
167 | ;; (which remains in REST). | |
41ea659a | 168 | (if (or rest list) |
288f95bd RS |
169 | (setq lists (cons (backquote-listify list (backquote-process rest)) |
170 | lists))) | |
cd320f32 RS |
171 | ;; Turn LISTS into a form that produces the combined list. |
172 | (setq expression | |
41ea659a | 173 | (if (or (cdr lists) |
cd320f32 | 174 | (eq (car-safe (car lists)) backquote-splice-symbol)) |
41ea659a RS |
175 | (cons 'append (nreverse lists)) |
176 | (car lists))) | |
cd320f32 | 177 | ;; Tack on any initial elements. |
41ea659a | 178 | (if firstlist |
cd320f32 RS |
179 | (setq expression (backquote-listify firstlist (cons 1 expression)))) |
180 | (if (eq (car-safe expression) 'quote) | |
41ea659a | 181 | (cons 0 (list 'quote s)) |
cd320f32 | 182 | (cons 1 expression)))))) |
41ea659a | 183 | |
288f95bd RS |
184 | ;; backquote-listify takes (tag . structure) pairs from backquote-process |
185 | ;; and decides between append, list, backquote-list*, and cons depending | |
41ea659a RS |
186 | ;; on which tags are in the list. |
187 | ||
288f95bd | 188 | (defun backquote-listify (list old-tail) |
41ea659a RS |
189 | (let ((heads nil) (tail (cdr old-tail)) (list-tail list) (item nil)) |
190 | (if (= (car old-tail) 0) | |
191 | (setq tail (eval tail) | |
192 | old-tail nil)) | |
193 | (while (consp list-tail) | |
194 | (setq item (car list-tail)) | |
195 | (setq list-tail (cdr list-tail)) | |
196 | (if (or heads old-tail (/= (car item) 0)) | |
197 | (setq heads (cons (cdr item) heads)) | |
198 | (setq tail (cons (eval (cdr item)) tail)))) | |
199 | (cond | |
200 | (tail | |
201 | (if (null old-tail) | |
202 | (setq tail (list 'quote tail))) | |
203 | (if heads | |
204 | (let ((use-list* (or (cdr heads) | |
205 | (and (consp (car heads)) | |
206 | (eq (car (car heads)) | |
207 | backquote-splice-symbol))))) | |
288f95bd | 208 | (cons (if use-list* 'backquote-list* 'cons) |
41ea659a RS |
209 | (append heads (list tail)))) |
210 | tail)) | |
211 | (t (cons 'list heads))))) | |
212 | ||
55535639 | 213 | ;;; backquote.el ends here |