diff --git a/library/ui/outliner.factor b/library/ui/outliner.factor
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+! Copyright (C) 2005 Slava Pestov.
+! See http://factor.sf.net/license.txt for BSD license.
+IN: gadgets-outliner
+USING: arrays gadgets gadgets-buttons gadgets-labels
+gadgets-layouts gadgets-panes gadgets-presentations generic io
+kernel sequences ;
+
+! Outliner widget.
+
+TUPLE: outliner gadget quot pile expanded? ;
+
+: add-outliner-node ( outliner -- )
+    dup outliner-gadget
+    swap outliner-pile add-gadget ;
+
+: setup-outliner ( quot outliner -- )
+    dup outliner-pile clear-gadget
+    dup outliner-gadget over outliner-pile add-gadget
+    over [ >r make-pane r> outliner-pile add-gadget ] [ 2drop ] if ;
+
+: collapse-outliner ( outliner -- )
+    f over set-outliner-expanded? f swap setup-outliner ;
+
+: expand-outliner ( outliner -- )
+    t over set-outliner-expanded?
+    dup outliner-quot swap setup-outliner ;
+
+: toggle-outliner ( outliner -- )
+    dup outliner-expanded?
+    [ collapse-outliner ] [ expand-outliner ] if ;
+
+: find-outliner [ outliner? ] find-parent ;
+
+: <expand-button> ( -- gadget )
+    "+" <label> [ find-outliner toggle-outliner ] <roll-button> ;
+
+C: outliner ( gadget quot -- gadget )
+    #! The quotation generates child gadgets.
+    [ set-outliner-quot ] keep
+    [ set-outliner-gadget ] keep
+    <shelf> over set-delegate
+    @{ 5 0 0 }@ over set-pack-gap
+    <expand-button> over add-gadget
+    <pile> over 2dup set-outliner-pile add-gadget
+    dup collapse-outliner ;