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special forms (save-excursion)
- To: Keisuke Nishida <kxn30 at po dot cwru dot edu>
- Subject: special forms (save-excursion)
- From: Kalle Olavi Niemitalo <tosi at stekt dot oulu dot fi>
- Date: 14 Mar 2000 22:42:42 +0200
- Cc: guile-emacs at sourceware dot cygnus dot com
How are you going to handle special forms in guile-emacs?
They can't be wrapped as easily as normal functions.
Will their C source be rewritten for Guile?
Below is a macro implementation of save-excursion.
I have tested it with:
(define (test)
(save-excursion
(goto-char (point-min))
(insert "hah")))
I also tried moving the mark-active-var binding to a separate let
between define-syntax and syntax-rules, but that didn't work out.
=================================================================
(use-syntax (ice-9 syncase))
(use-modules (emacs emacs)
(emacs import))
(define set-marker (emacs-import-function 'set-marker))
(define make-marker (emacs-import-function 'make-marker))
(define mark-marker (emacs-import-function 'mark-marker))
(define-syntax save-excursion
(syntax-rules ()
((save-excursion body ...)
(let ((mark-active-var (global-variable 'mark-active))
(outer-buffer *unspecified*)
(outer-point (make-marker))
(outer-mark (make-marker))
(outer-mark-active *unspecified*)
(inner-buffer #f) ; used as a first-time flag
(inner-point (make-marker))
(inner-mark (make-marker))
(inner-mark-active *unspecified*))
(dynamic-wind
(lambda ()
;; save outer state
(set! outer-buffer (current-buffer))
(set-marker outer-point (point))
(set-marker outer-mark (mark-marker))
(set! outer-mark-active (global-ref mark-active-var))
;; restore inner state, if any
(cond (inner-buffer
(set-buffer inner-buffer)
(goto-char inner-point)
(set-marker (mark-marker) inner-mark)
(global-set! mark-active-var inner-mark-active))))
(lambda ()
body ...)
(lambda ()
;; save inner state
(set! inner-buffer (current-buffer))
(set-marker inner-point (point))
(set-marker inner-mark (mark-marker))
(set! inner-mark-active (global-ref mark-active-var))
;; restore outer state
(set-buffer outer-buffer)
(goto-char outer-point)
(set-marker (mark-marker) outer-mark)
(global-set! mark-active-var outer-mark-active)))))))