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+;;; This file implements spans in terms of overlays, for emacs19.
+;;; Copyright (C) 1998 LFCS Edinburgh
+;;; Author: Healfdene Goguen
+
+;; Maintainer: LEGO Team <lego@dcs.ed.ac.uk>
+
+;; $Log$
+;; Revision 1.1  1998/09/03 13:51:34  da
+;; Renamed for new subdirectory structure
+;;
+;; Revision 2.0  1998/08/11 15:00:13  da
+;; New branch
+;;
+;; Revision 1.9  1998/06/10 14:02:39  hhg
+;; Wrote generic span functions for making spans read-only or read-write.
+;; Fixed bug in add-span and remove-span concerning return value of
+;; span-traverse.
+;;
+;; Revision 1.8  1998/06/10 12:41:47  hhg
+;; Compare span-end first rather than span-start in span-lt, because
+;; proof-lock-span is often changed and has starting point 1.
+;; Factored out common code of add-span and remove-span into
+;; span-traverse.
+;;
+;; Revision 1.7  1998/06/03 17:40:07  hhg
+;; Changed last-span to before-list.
+;; Added definitions of foldr and foldl if they aren't already loaded.
+;; Changed definitions of add-span, remove-span and find-span-aux to be
+;; non-recursive.
+;; Removed detach-extent since this file isn't used by xemacs.
+;; Added function append-unique to avoid repetitions in list generated by
+;; spans-at-region.
+;; Changed next-span so it uses member-if.
+;;
+;; Revision 1.6  1998/06/02 15:36:51  hhg
+;; Corrected comment about this being for emacs19.
+;;
+;; Revision 1.5  1998/05/29 09:50:10  tms
+;; o outsourced indentation to proof-indent
+;; o support indentation of commands
+;; o replaced test of Emacs version with availability test of specific
+;;   features
+;; o C-c C-c, C-c C-v and M-tab is now available in all buffers
+;;
+;; Revision 1.4  1998/05/21 17:27:41  hhg
+;; Removed uninitialized os variable in spans-at-region.
+;;
+;; Revision 1.3  1998/05/21 08:28:52  hhg
+;; Initialize 'before pointer in add-span-aux when last-span is nil.
+;; Removed span-at-type.
+;; Fixed bug in span-at-before, where (span-start span) may be nil.
+;; Added spans-at-(point|region)[-prop], which fixes bug of C-c u at end
+;; of buffer.
+;;
+;; Revision 1.2  1998/05/19 15:31:37  hhg
+;; Added header and log message.
+;; Fixed set-span-endpoints so it preserves invariant.
+;; Changed add-span and remove-span so that they update last-span
+;; correctly themselves, and don't take last-span as an argument.
+;;
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;               Bridging the emacs19/xemacs gulf                   ;;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; before-list represents a linked list of spans for each buffer.
+;; It has the invariants of:
+;; * being ordered wrt the starting point of the spans in the list,
+;;   with detached spans at the end.
+;; * not having overlapping overlays of the same type.
+
+(defvar before-list nil
+  "Start of backwards-linked list of spans")
+
+(make-variable-buffer-local 'before-list)
+
+
+(or (fboundp 'foldr)
+(defun foldr (func a seq)
+  "Return (func (func (func (... (func a Sn) ...) S2) S1) S0)
+when func's argument is 2 and seq is a sequence whose
+elements = S0 S1 S2 ... Sn. [tl-seq.el]"
+  (let ((i (length seq)))
+    (while (> i 0)
+      (setq i (1- i))
+      (setq a (funcall func a (elt seq i)))
+      )
+    a)))
+
+(or (fboundp 'foldl)
+(defun foldl (func a seq)
+  "Return (... (func (func (func a S0) S1) S2) ...)
+when func's argument is 2 and seq is a sequence whose
+elements = S0 S1 S2 .... [tl-seq.el]"
+  (let ((len (length seq))
+        (i 0))
+    (while (< i len)
+      (setq a (funcall func a (elt seq i)))
+      (setq i (1+ i))
+      )
+    a)))
+
+(defsubst span-start (span)
+  (overlay-start span))
+
+(defsubst span-end (span)
+  (overlay-end span))
+
+(defun set-span-property (span name value)
+  (overlay-put span name value))
+
+(defsubst span-property (span name)
+  (overlay-get span name))
+
+(defun span-read-only-hook (overlay after start end &optional len)
+  (error "Region is read-only"))
+
+(defun span-read-only (span)
+  (set-span-property span 'modification-hooks '(span-read-only-hook))
+  (set-span-property span 'insert-in-front-hooks '(span-read-only-hook)))
+
+(defun span-read-write (span)
+  (set-span-property span 'modification-hooks nil)
+  (set-span-property span 'insert-in-front-hooks nil))
+
+(defun int-nil-lt (m n)
+  (cond
+   ((eq m n) nil)
+   ((not n) t)
+   ((not m) nil)
+   (t (< m n))))
+
+;; We use end first because proof-locked-queue is often changed, and
+;; its starting point is always 1
+(defun span-lt (s u)
+  (or (int-nil-lt (span-end s) (span-end u))
+      (and (eq (span-end s) (span-end u))
+	   (int-nil-lt (span-start s) (span-start u)))))
+
+(defun span-traverse (span prop)
+  (cond
+   ((not before-list)
+    ;; before-list empty
+    'empty)
+   ((funcall prop before-list span)
+    ;; property holds for before-list and span
+    'hd)
+   (t
+    ;; traverse before-list for property
+    (let ((l before-list) (before (span-property before-list 'before)))
+      (while (and before (not (funcall prop before span)))
+	(setq l before)
+	(setq before (span-property before 'before)))
+      l))))
+
+(defun add-span (span)
+  (let ((ans (span-traverse span 'span-lt)))
+    (cond
+     ((eq ans 'empty)
+      (set-span-property span 'before nil)
+      (setq before-list span))
+     ((eq ans 'hd)
+      (set-span-property span 'before before-list)
+      (setq before-list span))
+     (t
+      (set-span-property span 'before
+			 (span-property ans 'before))
+      (set-span-property ans 'before span)))))
+
+(defun make-span (start end)
+  (add-span (make-overlay start end)))
+
+(defun remove-span (span)
+  (let ((ans (span-traverse span 'eq)))
+    (cond
+     ((eq ans 'empty)
+      (error "Bug: empty span list"))
+     ((eq ans 'hd)
+      (setq before-list (span-property before-list 'before)))
+     (ans
+      (set-span-property ans 'before (span-property span 'before)))
+     (t (error "Bug: span does not occur in span list")))))
+
+;; extent-at gives "smallest" extent at pos
+;; we're assuming right now that spans don't overlap
+(defun spans-at-point (pt)
+  (let ((overlays nil) (os nil))
+    (setq os (overlays-at pt))
+    (while os
+      (if (not (memq (car os) overlays))
+	  (setq overlays (cons (car os) overlays)))
+      (setq os (cdr os)))
+    overlays))
+
+;; assumes that there are no repetitions in l or m
+(defun append-unique (l m)
+  (foldl (lambda (n a) (if (memq a m) n (cons a n))) m l))
+
+(defun spans-at-region (start end)
+  (let ((overlays nil) (pos start))
+    (while (< pos end)
+      (setq overlays (append-unique (spans-at-point pos) overlays))
+      (setq pos (next-overlay-change pos)))
+    overlays))
+
+(defun spans-at-point-prop (pt prop)
+  (let ((f (cond
+	    (prop (lambda (spans span)
+		    (if (span-property span prop) (cons span spans)
+		      spans)))
+	    (t (lambda (spans span) (cons span spans))))))
+    (foldl f nil (spans-at-point pt))))
+
+(defun spans-at-region-prop (start end prop)
+  (let ((f (cond
+	    (prop (lambda (spans span)
+		    (if (span-property span prop) (cons span spans)
+		      spans)))
+	    (t (lambda (spans span) (cons span spans))))))
+    (foldl f nil (spans-at-region start end))))
+
+(defun span-at (pt prop)
+  (car (spans-at-point-prop pt prop)))
+
+(defsubst detach-span (span)
+  (remove-span span)
+  (delete-overlay span)
+  (add-span span))
+
+(defsubst delete-span (span)
+  (remove-span span)
+  (delete-overlay span))
+
+;; The next two change ordering of list of spans:
+(defsubst set-span-endpoints (span start end)
+  (remove-span span)
+  (move-overlay span start end)
+  (add-span span))
+
+(defsubst set-span-start (span value)
+  (set-span-endpoints span value (span-end span)))
+
+;; This doesn't affect invariant:
+(defsubst set-span-end (span value)
+  (set-span-endpoints span (span-start span) value))
+
+(defsubst delete-spans (start end prop)
+  (mapcar 'delete-span (spans-at-region-prop start end prop)))
+
+(defun map-spans-aux (f l)
+  (cond (l (cons (funcall f l) (map-spans-aux f (span-property l 'before))))
+	(t ())))
+
+(defsubst map-spans (f)
+  (map-spans-aux f before-list))
+
+(defun find-span-aux (prop-p l)
+  (while (and l (not (funcall prop-p l)))
+       (setq l (span-property l 'before)))
+     l)
+
+(defun find-span (prop-p)
+  (find-span-aux prop-p before-list))
+
+(defun span-at-before (pt prop)
+  (let ((prop-pt-p
+	 (cond (prop (lambda (span)
+		       (let ((start (span-start span)))
+			 (and start (> pt start)
+			    (span-property span prop)))))
+	       (t (lambda (span)
+		    (let ((start (span-start span)))
+		      (and start (> pt start))))))))
+    (find-span prop-pt-p)))
+  
+(defun prev-span (span prop)
+  (let ((prev-prop-p
+	 (cond (prop (lambda (span) (span-property span prop)))
+	       (t (lambda (span) t)))))
+    (find-span-aux prev-prop-p (span-property span 'before))))
+
+;; overlays are [start, end)
+;; If there are two spans overlapping then this won't work.
+(defun next-span (span prop)
+  (let ((l (member-if (lambda (span) (span-property span prop))
+		       (overlays-at
+			(next-overlay-change (overlay-start span))))))
+    (if l (car l) nil)))
+
+
+(provide 'span-overlay)