Re: [MIT-Scheme-devel] forcing left-insertion or right-insertion in Edwin

[Taylor R. Campbell]

The obvious solution is to mimic SAVE-EXCURSION, but to make a
right-inserting copy of the point instead of a left-inserting copy.
Why does SAVE-EXCURSION make a left-inserting copy of the point, but a
right-inserting copy of the mark?

This definition of SAVE-EXCURSION makes more sense to me, and more
closely mirrors that in GNU Emacs:

  (define (save-excursion thunk)
    (let ((point) (mark))
      (dynamic-wind
       (lambda ()
         (set! point (mark-right-inserting-copy (current-point)))
         (set! mark (mark-right-inserting-copy (current-mark))))
       thunk
       (lambda ()
         (let ((point (set! point))
               (mark (set! mark)))
           (let ((buffer (mark-buffer point)))
             (if (buffer-alive? buffer)
                 (begin (select-buffer buffer)
                        (set-current-point! point)
                        (set-current-mark! mark)))))))))