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b035a678 | 1 | ;;; backquote.el --- implement the ` Lisp construct |
b578f267 | 2 | |
ba318903 | 3 | ;; Copyright (C) 1990, 1992, 1994, 2001-2014 Free Software Foundation, |
ab422c4d | 4 | ;; Inc. |
c0274f38 | 5 | |
41ea659a | 6 | ;; Author: Rick Sladkey <jrs@world.std.com> |
34dc21db | 7 | ;; Maintainer: emacs-devel@gnu.org |
41ea659a | 8 | ;; Keywords: extensions, internal |
bd78fa1d | 9 | ;; Package: emacs |
9750e079 | 10 | |
be010748 | 11 | ;; This file is part of GNU Emacs. |
c440e42b | 12 | |
d6cba7ae | 13 | ;; GNU Emacs is free software: you can redistribute it and/or modify |
c440e42b | 14 | ;; it under the terms of the GNU General Public License as published by |
d6cba7ae GM |
15 | ;; the Free Software Foundation, either version 3 of the License, or |
16 | ;; (at your option) any later version. | |
c440e42b RS |
17 | |
18 | ;; GNU Emacs is distributed in the hope that it will be useful, | |
19 | ;; but WITHOUT ANY WARRANTY; without even the implied warranty of | |
20 | ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
21 | ;; GNU General Public License for more details. | |
22 | ||
23 | ;; You should have received a copy of the GNU General Public License | |
d6cba7ae | 24 | ;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>. |
c440e42b | 25 | |
be010748 | 26 | ;;; Commentary: |
41ea659a | 27 | |
574cb02e RS |
28 | ;; When the Lisp reader sees `(...), it generates (\` (...)). |
29 | ;; When it sees ,... inside such a backquote form, it generates (\, ...). | |
30 | ;; For ,@... it generates (\,@ ...). | |
31 | ||
288f95bd | 32 | ;; This backquote will generate calls to the backquote-list* form. |
41ea659a RS |
33 | ;; Both a function version and a macro version are included. |
34 | ;; The macro version is used by default because it is faster | |
35 | ;; and needs no run-time support. It should really be a subr. | |
c440e42b | 36 | |
e5167999 | 37 | ;;; Code: |
c440e42b | 38 | |
49116ac0 JB |
39 | (provide 'backquote) |
40 | ||
288f95bd | 41 | ;; function and macro versions of backquote-list* |
41ea659a | 42 | |
288f95bd | 43 | (defun backquote-list*-function (first &rest list) |
41ea659a RS |
44 | "Like `list' but the last argument is the tail of the new list. |
45 | ||
288f95bd | 46 | For example (backquote-list* 'a 'b 'c) => (a b . c)" |
1de9630d SM |
47 | ;; The recursive solution is much nicer: |
48 | ;; (if list (cons first (apply 'backquote-list*-function list)) first)) | |
49 | ;; but Emacs is not very good at efficiently processing recursion. | |
41ea659a RS |
50 | (if list |
51 | (let* ((rest list) (newlist (cons first nil)) (last newlist)) | |
52 | (while (cdr rest) | |
53 | (setcdr last (cons (car rest) nil)) | |
54 | (setq last (cdr last) | |
55 | rest (cdr rest))) | |
56 | (setcdr last (car rest)) | |
57 | newlist) | |
58 | first)) | |
59 | ||
288f95bd RS |
60 | (defmacro backquote-list*-macro (first &rest list) |
61 | "Like `list' but the last argument is the tail of the new list. | |
41ea659a | 62 | |
288f95bd | 63 | For example (backquote-list* 'a 'b 'c) => (a b . c)" |
1de9630d SM |
64 | ;; The recursive solution is much nicer: |
65 | ;; (if list (list 'cons first (cons 'backquote-list*-macro list)) first)) | |
66 | ;; but Emacs is not very good at efficiently processing such things. | |
67 | (setq list (nreverse (cons first list)) | |
41ea659a RS |
68 | first (car list) |
69 | list (cdr list)) | |
70 | (if list | |
71 | (let* ((second (car list)) | |
72 | (rest (cdr list)) | |
73 | (newlist (list 'cons second first))) | |
74 | (while rest | |
75 | (setq newlist (list 'cons (car rest) newlist) | |
76 | rest (cdr rest))) | |
77 | newlist) | |
78 | first)) | |
79 | ||
c9c7f2c4 | 80 | (defalias 'backquote-list* (symbol-function 'backquote-list*-macro)) |
41ea659a RS |
81 | |
82 | ;; A few advertised variables that control which symbols are used | |
83 | ;; to represent the backquote, unquote, and splice operations. | |
4c548238 | 84 | (defconst backquote-backquote-symbol '\` |
cdab3e50 | 85 | "Symbol used to represent a backquote or nested backquote.") |
4c548238 | 86 | |
727fb8cc | 87 | (defconst backquote-unquote-symbol '\, |
cdab3e50 | 88 | "Symbol used to represent an unquote inside a backquote.") |
4c548238 | 89 | |
727fb8cc | 90 | (defconst backquote-splice-symbol '\,@ |
cdab3e50 | 91 | "Symbol used to represent a splice inside a backquote.") |
41ea659a | 92 | |
82bb5643 | 93 | (defmacro backquote (structure) |
41ea659a RS |
94 | "Argument STRUCTURE describes a template to build. |
95 | ||
96 | The whole structure acts as if it were quoted except for certain | |
97 | places where expressions are evaluated and inserted or spliced in. | |
98 | ||
99 | For example: | |
100 | ||
1df90f8f RS |
101 | b => (ba bb bc) ; assume b has this value |
102 | `(a b c) => (a b c) ; backquote acts like quote | |
2b1c5e12 RS |
103 | `(a ,b c) => (a (ba bb bc) c) ; insert the value of b |
104 | `(a ,@b c) => (a ba bb bc c) ; splice in the value of b | |
41ea659a | 105 | |
288f95bd | 106 | Vectors work just like lists. Nested backquotes are permitted." |
82bb5643 | 107 | (cdr (backquote-process structure))) |
41ea659a RS |
108 | |
109 | ;; GNU Emacs has no reader macros | |
110 | ||
1df90f8f | 111 | (defalias '\` (symbol-function 'backquote)) |
41ea659a | 112 | |
288f95bd | 113 | ;; backquote-process returns a dotted-pair of a tag (0, 1, or 2) and |
41ea659a RS |
114 | ;; the backquote-processed structure. 0 => the structure is |
115 | ;; constant, 1 => to be unquoted, 2 => to be spliced in. | |
116 | ;; The top-level backquote macro just discards the tag. | |
117 | ||
3527bdcc SM |
118 | (defun backquote-delay-process (s level) |
119 | "Process a (un|back|splice)quote inside a backquote. | |
120 | This simply recurses through the body." | |
5d3440f4 SM |
121 | (let ((exp (backquote-listify (list (cons 0 (list 'quote (car s)))) |
122 | (backquote-process (cdr s) level)))) | |
3527bdcc SM |
123 | (if (eq (car-safe exp) 'quote) |
124 | (cons 0 (list 'quote s)) | |
125 | (cons 1 exp)))) | |
126 | ||
127 | (defun backquote-process (s &optional level) | |
128 | "Process the body of a backquote. | |
129 | S is the body. Returns a cons cell whose cdr is piece of code which | |
130 | is the macro-expansion of S, and whose car is a small integer whose value | |
131 | can either indicate that the code is constant (0), or not (1), or returns | |
132 | a list which should be spliced into its environment (2). | |
133 | LEVEL is only used internally and indicates the nesting level: | |
134 | 0 (the default) is for the toplevel nested inside a single backquote." | |
135 | (unless level (setq level 0)) | |
41ea659a RS |
136 | (cond |
137 | ((vectorp s) | |
3527bdcc | 138 | (let ((n (backquote-process (append s ()) level))) |
41ea659a RS |
139 | (if (= (car n) 0) |
140 | (cons 0 s) | |
141 | (cons 1 (cond | |
ea4a56de RS |
142 | ((not (listp (cdr n))) |
143 | (list 'vconcat (cdr n))) | |
41ea659a RS |
144 | ((eq (nth 1 n) 'list) |
145 | (cons 'vector (nthcdr 2 n))) | |
146 | ((eq (nth 1 n) 'append) | |
147 | (cons 'vconcat (nthcdr 2 n))) | |
148 | (t | |
149 | (list 'apply '(function vector) (cdr n)))))))) | |
150 | ((atom s) | |
151 | (cons 0 (if (or (null s) (eq s t) (not (symbolp s))) | |
152 | s | |
153 | (list 'quote s)))) | |
154 | ((eq (car s) backquote-unquote-symbol) | |
3527bdcc | 155 | (if (<= level 0) |
f2223371 SM |
156 | (if (> (length s) 2) |
157 | ;; We could support it with: (cons 2 `(list . ,(cdr s))) | |
158 | ;; But let's not encourage such uses. | |
159 | (error "Multiple args to , are not supported: %S" s) | |
160 | (cons 1 (nth 1 s))) | |
3527bdcc | 161 | (backquote-delay-process s (1- level)))) |
41ea659a | 162 | ((eq (car s) backquote-splice-symbol) |
3527bdcc | 163 | (if (<= level 0) |
f2223371 SM |
164 | (if (> (length s) 2) |
165 | ;; (cons 2 `(append . ,(cdr s))) | |
166 | (error "Multiple args to ,@ are not supported: %S" s) | |
167 | (cons 2 (nth 1 s))) | |
3527bdcc | 168 | (backquote-delay-process s (1- level)))) |
41ea659a | 169 | ((eq (car s) backquote-backquote-symbol) |
3527bdcc | 170 | (backquote-delay-process s (1+ level))) |
41ea659a | 171 | (t |
cd320f32 RS |
172 | (let ((rest s) |
173 | item firstlist list lists expression) | |
174 | ;; Scan this list-level, setting LISTS to a list of forms, | |
175 | ;; each of which produces a list of elements | |
176 | ;; that should go in this level. | |
a1506d29 | 177 | ;; The order of LISTS is backwards. |
cd320f32 RS |
178 | ;; If there are non-splicing elements (constant or variable) |
179 | ;; at the beginning, put them in FIRSTLIST, | |
180 | ;; as a list of tagged values (TAG . FORM). | |
181 | ;; If there are any at the end, they go in LIST, likewise. | |
3527bdcc SM |
182 | (while (and (consp rest) |
183 | ;; Stop if the cdr is an expression inside a backquote or | |
184 | ;; unquote since this needs to go recursively through | |
185 | ;; backquote-process. | |
186 | (not (or (eq (car rest) backquote-unquote-symbol) | |
187 | (eq (car rest) backquote-backquote-symbol)))) | |
188 | (setq item (backquote-process (car rest) level)) | |
41ea659a RS |
189 | (cond |
190 | ((= (car item) 2) | |
1d08cb50 RS |
191 | ;; Put the nonspliced items before the first spliced item |
192 | ;; into FIRSTLIST. | |
193 | (if (null lists) | |
41ea659a RS |
194 | (setq firstlist list |
195 | list nil)) | |
1d08cb50 | 196 | ;; Otherwise, put any preceding nonspliced items into LISTS. |
41ea659a | 197 | (if list |
3527bdcc SM |
198 | (push (backquote-listify list '(0 . nil)) lists)) |
199 | (push (cdr item) lists) | |
41ea659a RS |
200 | (setq list nil)) |
201 | (t | |
202 | (setq list (cons item list)))) | |
203 | (setq rest (cdr rest))) | |
cd320f32 RS |
204 | ;; Handle nonsplicing final elements, and the tail of the list |
205 | ;; (which remains in REST). | |
41ea659a | 206 | (if (or rest list) |
3527bdcc SM |
207 | (push (backquote-listify list (backquote-process rest level)) |
208 | lists)) | |
a1506d29 | 209 | ;; Turn LISTS into a form that produces the combined list. |
cd320f32 | 210 | (setq expression |
41ea659a | 211 | (if (or (cdr lists) |
cd320f32 | 212 | (eq (car-safe (car lists)) backquote-splice-symbol)) |
41ea659a RS |
213 | (cons 'append (nreverse lists)) |
214 | (car lists))) | |
cd320f32 | 215 | ;; Tack on any initial elements. |
41ea659a | 216 | (if firstlist |
cd320f32 RS |
217 | (setq expression (backquote-listify firstlist (cons 1 expression)))) |
218 | (if (eq (car-safe expression) 'quote) | |
41ea659a | 219 | (cons 0 (list 'quote s)) |
cd320f32 | 220 | (cons 1 expression)))))) |
41ea659a | 221 | |
288f95bd RS |
222 | ;; backquote-listify takes (tag . structure) pairs from backquote-process |
223 | ;; and decides between append, list, backquote-list*, and cons depending | |
41ea659a RS |
224 | ;; on which tags are in the list. |
225 | ||
288f95bd | 226 | (defun backquote-listify (list old-tail) |
41ea659a RS |
227 | (let ((heads nil) (tail (cdr old-tail)) (list-tail list) (item nil)) |
228 | (if (= (car old-tail) 0) | |
229 | (setq tail (eval tail) | |
230 | old-tail nil)) | |
231 | (while (consp list-tail) | |
232 | (setq item (car list-tail)) | |
233 | (setq list-tail (cdr list-tail)) | |
234 | (if (or heads old-tail (/= (car item) 0)) | |
235 | (setq heads (cons (cdr item) heads)) | |
236 | (setq tail (cons (eval (cdr item)) tail)))) | |
237 | (cond | |
238 | (tail | |
239 | (if (null old-tail) | |
240 | (setq tail (list 'quote tail))) | |
241 | (if heads | |
242 | (let ((use-list* (or (cdr heads) | |
243 | (and (consp (car heads)) | |
244 | (eq (car (car heads)) | |
245 | backquote-splice-symbol))))) | |
288f95bd | 246 | (cons (if use-list* 'backquote-list* 'cons) |
41ea659a RS |
247 | (append heads (list tail)))) |
248 | tail)) | |
249 | (t (cons 'list heads))))) | |
250 | ||
55535639 | 251 | ;;; backquote.el ends here |