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be010748 | 1 | ;;; backquote.el -- implement the ` Lisp construct |
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 | |
be010748 | 8 | ;; This file is part of GNU Emacs. |
c440e42b RS |
9 | |
10 | ;; GNU Emacs is free software; you can redistribute it and/or modify | |
11 | ;; it under the terms of the GNU General Public License as published by | |
7c938215 | 12 | ;; the Free Software Foundation; either version 2, or (at your option) |
c440e42b RS |
13 | ;; any later version. |
14 | ||
15 | ;; GNU Emacs is distributed in the hope that it will be useful, | |
16 | ;; but WITHOUT ANY WARRANTY; without even the implied warranty of | |
17 | ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
18 | ;; GNU General Public License for more details. | |
19 | ||
20 | ;; You should have received a copy of the GNU General Public License | |
21 | ;; along with GNU Emacs; see the file COPYING. If not, write to | |
22 | ;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. | |
23 | ||
be010748 | 24 | ;;; Commentary: |
41ea659a | 25 | |
288f95bd | 26 | ;; This backquote will generate calls to the backquote-list* form. |
41ea659a RS |
27 | ;; Both a function version and a macro version are included. |
28 | ;; The macro version is used by default because it is faster | |
29 | ;; and needs no run-time support. It should really be a subr. | |
c440e42b | 30 | |
e5167999 | 31 | ;;; Code: |
c440e42b | 32 | |
49116ac0 JB |
33 | (provide 'backquote) |
34 | ||
288f95bd | 35 | ;; function and macro versions of backquote-list* |
41ea659a | 36 | |
288f95bd | 37 | (defun backquote-list*-function (first &rest list) |
41ea659a RS |
38 | "Like `list' but the last argument is the tail of the new list. |
39 | ||
288f95bd | 40 | For example (backquote-list* 'a 'b 'c) => (a b . c)" |
41ea659a RS |
41 | (if list |
42 | (let* ((rest list) (newlist (cons first nil)) (last newlist)) | |
43 | (while (cdr rest) | |
44 | (setcdr last (cons (car rest) nil)) | |
45 | (setq last (cdr last) | |
46 | rest (cdr rest))) | |
47 | (setcdr last (car rest)) | |
48 | newlist) | |
49 | first)) | |
50 | ||
288f95bd RS |
51 | (defmacro backquote-list*-macro (first &rest list) |
52 | "Like `list' but the last argument is the tail of the new list. | |
41ea659a | 53 | |
288f95bd | 54 | For example (backquote-list* 'a 'b 'c) => (a b . c)" |
41ea659a RS |
55 | (setq list (reverse (cons first list)) |
56 | first (car list) | |
57 | list (cdr list)) | |
58 | (if list | |
59 | (let* ((second (car list)) | |
60 | (rest (cdr list)) | |
61 | (newlist (list 'cons second first))) | |
62 | (while rest | |
63 | (setq newlist (list 'cons (car rest) newlist) | |
64 | rest (cdr rest))) | |
65 | newlist) | |
66 | first)) | |
67 | ||
c9c7f2c4 | 68 | (defalias 'backquote-list* (symbol-function 'backquote-list*-macro)) |
41ea659a RS |
69 | |
70 | ;; A few advertised variables that control which symbols are used | |
71 | ;; to represent the backquote, unquote, and splice operations. | |
72 | ||
1df90f8f | 73 | (defvar backquote-backquote-symbol '\` |
41ea659a RS |
74 | "*Symbol used to represent a backquote or nested backquote (e.g. `).") |
75 | ||
76 | (defvar backquote-unquote-symbol ', | |
288f95bd | 77 | "*Symbol used to represent an unquote (e.g. `,') inside a backquote.") |
41ea659a RS |
78 | |
79 | (defvar backquote-splice-symbol ',@ | |
44c48a83 | 80 | "*Symbol used to represent a splice (e.g. `,@') inside a backquote.") |
41ea659a | 81 | |
325e3af2 | 82 | ;;;###autoload |
41ea659a RS |
83 | (defmacro backquote (arg) |
84 | "Argument STRUCTURE describes a template to build. | |
85 | ||
86 | The whole structure acts as if it were quoted except for certain | |
87 | places where expressions are evaluated and inserted or spliced in. | |
88 | ||
89 | For example: | |
90 | ||
1df90f8f RS |
91 | b => (ba bb bc) ; assume b has this value |
92 | `(a b c) => (a b c) ; backquote acts like quote | |
2b1c5e12 RS |
93 | `(a ,b c) => (a (ba bb bc) c) ; insert the value of b |
94 | `(a ,@b c) => (a ba bb bc c) ; splice in the value of b | |
41ea659a | 95 | |
288f95bd RS |
96 | Vectors work just like lists. Nested backquotes are permitted." |
97 | (cdr (backquote-process arg))) | |
41ea659a RS |
98 | |
99 | ;; GNU Emacs has no reader macros | |
100 | ||
325e3af2 | 101 | ;;;###autoload |
1df90f8f | 102 | (defalias '\` (symbol-function 'backquote)) |
41ea659a | 103 | |
288f95bd | 104 | ;; backquote-process returns a dotted-pair of a tag (0, 1, or 2) and |
41ea659a RS |
105 | ;; the backquote-processed structure. 0 => the structure is |
106 | ;; constant, 1 => to be unquoted, 2 => to be spliced in. | |
107 | ;; The top-level backquote macro just discards the tag. | |
108 | ||
288f95bd | 109 | (defun backquote-process (s) |
41ea659a RS |
110 | (cond |
111 | ((vectorp s) | |
288f95bd | 112 | (let ((n (backquote-process (append s ())))) |
41ea659a RS |
113 | (if (= (car n) 0) |
114 | (cons 0 s) | |
115 | (cons 1 (cond | |
116 | ((eq (nth 1 n) 'list) | |
117 | (cons 'vector (nthcdr 2 n))) | |
118 | ((eq (nth 1 n) 'append) | |
119 | (cons 'vconcat (nthcdr 2 n))) | |
120 | (t | |
121 | (list 'apply '(function vector) (cdr n)))))))) | |
122 | ((atom s) | |
123 | (cons 0 (if (or (null s) (eq s t) (not (symbolp s))) | |
124 | s | |
125 | (list 'quote s)))) | |
126 | ((eq (car s) backquote-unquote-symbol) | |
127 | (cons 1 (nth 1 s))) | |
128 | ((eq (car s) backquote-splice-symbol) | |
129 | (cons 2 (nth 1 s))) | |
130 | ((eq (car s) backquote-backquote-symbol) | |
288f95bd | 131 | (backquote-process (cdr (backquote-process (nth 1 s))))) |
41ea659a | 132 | (t |
cd320f32 RS |
133 | (let ((rest s) |
134 | item firstlist list lists expression) | |
135 | ;; Scan this list-level, setting LISTS to a list of forms, | |
136 | ;; each of which produces a list of elements | |
137 | ;; that should go in this level. | |
138 | ;; The order of LISTS is backwards. | |
139 | ;; If there are non-splicing elements (constant or variable) | |
140 | ;; at the beginning, put them in FIRSTLIST, | |
141 | ;; as a list of tagged values (TAG . FORM). | |
142 | ;; If there are any at the end, they go in LIST, likewise. | |
41ea659a | 143 | (while (consp rest) |
cd320f32 | 144 | ;; Turn . (, foo) into (,@ foo). |
41ea659a RS |
145 | (if (eq (car rest) backquote-unquote-symbol) |
146 | (setq rest (list (list backquote-splice-symbol (nth 1 rest))))) | |
288f95bd | 147 | (setq item (backquote-process (car rest))) |
41ea659a RS |
148 | (cond |
149 | ((= (car item) 2) | |
1d08cb50 RS |
150 | ;; Put the nonspliced items before the first spliced item |
151 | ;; into FIRSTLIST. | |
152 | (if (null lists) | |
41ea659a RS |
153 | (setq firstlist list |
154 | list nil)) | |
1d08cb50 | 155 | ;; Otherwise, put any preceding nonspliced items into LISTS. |
41ea659a | 156 | (if list |
288f95bd | 157 | (setq lists (cons (backquote-listify list '(0 . nil)) lists))) |
41ea659a RS |
158 | (setq lists (cons (cdr item) lists)) |
159 | (setq list nil)) | |
160 | (t | |
161 | (setq list (cons item list)))) | |
162 | (setq rest (cdr rest))) | |
cd320f32 RS |
163 | ;; Handle nonsplicing final elements, and the tail of the list |
164 | ;; (which remains in REST). | |
41ea659a | 165 | (if (or rest list) |
288f95bd RS |
166 | (setq lists (cons (backquote-listify list (backquote-process rest)) |
167 | lists))) | |
cd320f32 RS |
168 | ;; Turn LISTS into a form that produces the combined list. |
169 | (setq expression | |
41ea659a | 170 | (if (or (cdr lists) |
cd320f32 | 171 | (eq (car-safe (car lists)) backquote-splice-symbol)) |
41ea659a RS |
172 | (cons 'append (nreverse lists)) |
173 | (car lists))) | |
cd320f32 | 174 | ;; Tack on any initial elements. |
41ea659a | 175 | (if firstlist |
cd320f32 RS |
176 | (setq expression (backquote-listify firstlist (cons 1 expression)))) |
177 | (if (eq (car-safe expression) 'quote) | |
41ea659a | 178 | (cons 0 (list 'quote s)) |
cd320f32 | 179 | (cons 1 expression)))))) |
41ea659a | 180 | |
288f95bd RS |
181 | ;; backquote-listify takes (tag . structure) pairs from backquote-process |
182 | ;; and decides between append, list, backquote-list*, and cons depending | |
41ea659a RS |
183 | ;; on which tags are in the list. |
184 | ||
288f95bd | 185 | (defun backquote-listify (list old-tail) |
41ea659a RS |
186 | (let ((heads nil) (tail (cdr old-tail)) (list-tail list) (item nil)) |
187 | (if (= (car old-tail) 0) | |
188 | (setq tail (eval tail) | |
189 | old-tail nil)) | |
190 | (while (consp list-tail) | |
191 | (setq item (car list-tail)) | |
192 | (setq list-tail (cdr list-tail)) | |
193 | (if (or heads old-tail (/= (car item) 0)) | |
194 | (setq heads (cons (cdr item) heads)) | |
195 | (setq tail (cons (eval (cdr item)) tail)))) | |
196 | (cond | |
197 | (tail | |
198 | (if (null old-tail) | |
199 | (setq tail (list 'quote tail))) | |
200 | (if heads | |
201 | (let ((use-list* (or (cdr heads) | |
202 | (and (consp (car heads)) | |
203 | (eq (car (car heads)) | |
204 | backquote-splice-symbol))))) | |
288f95bd | 205 | (cons (if use-list* 'backquote-list* 'cons) |
41ea659a RS |
206 | (append heads (list tail)))) |
207 | tail)) | |
208 | (t (cons 'list heads))))) | |
209 | ||
210 | ;; backquote.el ends here |