mirror of
https://git.savannah.gnu.org/git/emacs.git
synced 2024-11-29 07:58:28 +00:00
224 lines
7.5 KiB
EmacsLisp
224 lines
7.5 KiB
EmacsLisp
;;; New backquote for GNU Emacs.
|
|
;;; Copyright (C) 1990, 1992, 1994 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.
|
|
|
|
;; 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 2, or (at your option)
|
|
;; any later version.
|
|
|
|
;; GNU Emacs is distributed in the hope that it will be useful,
|
|
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
;; 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.
|
|
|
|
;; This backquote will generate calls to the backquote-list* form.
|
|
;; Both a function version and a macro version are included.
|
|
;; The macro version is used by default because it is faster
|
|
;; and needs no run-time support. It should really be a subr.
|
|
|
|
;;; Code:
|
|
|
|
(provide 'backquote)
|
|
|
|
;; function and macro versions of backquote-list*
|
|
|
|
(defun backquote-list*-function (first &rest list)
|
|
"Like `list' but the last argument is the tail of the new list.
|
|
|
|
For example (backquote-list* 'a 'b 'c) => (a b . c)"
|
|
(if list
|
|
(let* ((rest list) (newlist (cons first nil)) (last newlist))
|
|
(while (cdr rest)
|
|
(setcdr last (cons (car rest) nil))
|
|
(setq last (cdr last)
|
|
rest (cdr rest)))
|
|
(setcdr last (car rest))
|
|
newlist)
|
|
first))
|
|
|
|
(defmacro backquote-list*-macro (first &rest list)
|
|
"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))
|
|
first (car list)
|
|
list (cdr list))
|
|
(if list
|
|
(let* ((second (car list))
|
|
(rest (cdr list))
|
|
(newlist (list 'cons second first)))
|
|
(while rest
|
|
(setq newlist (list 'cons (car rest) newlist)
|
|
rest (cdr rest)))
|
|
newlist)
|
|
first))
|
|
|
|
(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.
|
|
|
|
(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.")
|
|
|
|
(defvar backquote-splice-symbol ',@
|
|
"*Symbol used to represent a splice (e.g. `,@') inside a backquote.")
|
|
|
|
;;;###autoload
|
|
(defmacro backquote (arg)
|
|
"Argument STRUCTURE describes a template to build.
|
|
|
|
The whole structure acts as if it were quoted except for certain
|
|
places where expressions are evaluated and inserted or spliced in.
|
|
|
|
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
|
|
|
|
Vectors work just like lists. Nested backquotes are permitted."
|
|
(cdr (backquote-process arg)))
|
|
|
|
;; GNU Emacs has no reader macros
|
|
|
|
;;;###autoload
|
|
(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
|
|
;; constant, 1 => to be unquoted, 2 => to be spliced in.
|
|
;; The top-level backquote macro just discards the tag.
|
|
|
|
(defun backquote-process (s)
|
|
(cond
|
|
((vectorp s)
|
|
(let ((n (backquote-process (append s ()))))
|
|
(if (= (car n) 0)
|
|
(cons 0 s)
|
|
(cons 1 (cond
|
|
((eq (nth 1 n) 'list)
|
|
(cons 'vector (nthcdr 2 n)))
|
|
((eq (nth 1 n) 'append)
|
|
(cons 'vconcat (nthcdr 2 n)))
|
|
(t
|
|
(list 'apply '(function vector) (cdr n))))))))
|
|
((atom s)
|
|
(cons 0 (if (or (null s) (eq s t) (not (symbolp s)))
|
|
s
|
|
(list 'quote s))))
|
|
((eq (car s) backquote-unquote-symbol)
|
|
(cons 1 (nth 1 s)))
|
|
((eq (car s) backquote-splice-symbol)
|
|
(cons 2 (nth 1 s)))
|
|
((eq (car s) backquote-backquote-symbol)
|
|
(backquote-process (cdr (backquote-process (nth 1 s)))))
|
|
(t
|
|
(let ((rest s)
|
|
item firstlist list lists expression)
|
|
;; 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.
|
|
;; If there are non-splicing elements (constant or variable)
|
|
;; at the beginning, put them in FIRSTLIST,
|
|
;; as a list of tagged values (TAG . FORM).
|
|
;; If there are any at the end, they go in LIST, likewise.
|
|
(while (consp rest)
|
|
;; Turn . (, foo) into (,@ foo).
|
|
(if (eq (car rest) backquote-unquote-symbol)
|
|
(setq rest (list (list backquote-splice-symbol (nth 1 rest)))))
|
|
(setq item (backquote-process (car rest)))
|
|
(cond
|
|
((= (car item) 2)
|
|
;; 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))
|
|
(setq list nil))
|
|
(t
|
|
(setq list (cons item list))))
|
|
(setq rest (cdr rest)))
|
|
;; Handle nonsplicing final elements, and the tail of the list
|
|
;; (which remains in REST).
|
|
(if (or rest list)
|
|
(setq lists (cons (backquote-listify list (backquote-process rest))
|
|
lists)))
|
|
;; Turn LISTS into a form that produces the combined list.
|
|
(setq expression
|
|
(if (or (cdr lists)
|
|
(eq (car-safe (car lists)) backquote-splice-symbol))
|
|
(cons 'append (nreverse lists))
|
|
(car lists)))
|
|
;; Tack on any initial elements.
|
|
(if firstlist
|
|
(setq expression (backquote-listify firstlist (cons 1 expression))))
|
|
(if (eq (car-safe expression) 'quote)
|
|
(cons 0 (list 'quote s))
|
|
(cons 1 expression))))))
|
|
|
|
;; backquote-listify takes (tag . structure) pairs from backquote-process
|
|
;; and decides between append, list, backquote-list*, and cons depending
|
|
;; on which tags are in the list.
|
|
|
|
(defun backquote-listify (list old-tail)
|
|
(let ((heads nil) (tail (cdr old-tail)) (list-tail list) (item nil))
|
|
(if (= (car old-tail) 0)
|
|
(setq tail (eval tail)
|
|
old-tail nil))
|
|
(while (consp list-tail)
|
|
(setq item (car list-tail))
|
|
(setq list-tail (cdr list-tail))
|
|
(if (or heads old-tail (/= (car item) 0))
|
|
(setq heads (cons (cdr item) heads))
|
|
(setq tail (cons (eval (cdr item)) tail))))
|
|
(cond
|
|
(tail
|
|
(if (null old-tail)
|
|
(setq tail (list 'quote tail)))
|
|
(if heads
|
|
(let ((use-list* (or (cdr heads)
|
|
(and (consp (car heads))
|
|
(eq (car (car heads))
|
|
backquote-splice-symbol)))))
|
|
(cons (if use-list* 'backquote-list* 'cons)
|
|
(append heads (list tail))))
|
|
tail))
|
|
(t (cons 'list heads)))))
|
|
|
|
;; backquote.el ends here
|