diff --git a/library/ui/tools/walker.factor b/library/ui/tools/walker.factor
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+! Copyright (C) 2006 Slava Pestov.
+! See http://factorcode.org/license.txt for BSD license.
+IN: gadgets-walker
+USING: gadgets gadgets-buttons gadgets-frames gadgets-listener
+gadgets-panes gadgets-scrolling gadgets-text gadgets-tiles
+gadgets-tracks generic inspector interpreter io kernel listener
+math models namespaces sequences shells threads ;
+
+TUPLE: stack-track ;
+
+C: stack-track ( cs rs ds -- gadget )
+    {
+        { [ "Data stack"   <stack-tile> ] f f 1/3 }
+        { [ "Retain stack" <stack-tile> ] f f 1/3 }
+        { [ [ callstack. ] "Call stack" <pane-tile> ] f f 1/3 }
+    } { 1 0 } make-track* ;
+
+TUPLE: walker-track pane input ;
+
+: <quotation-display> ( quot -- gadget )
+    [ [ first2 callframe. ] when* ] <pane-control> <scroller> ;
+
+: <walker-input> ( -- gadget )
+    gadget get walker-track-pane <interactor> ;
+
+C: walker-track ( cs rs ds quot -- gadget )
+    {
+        { [ <quotation-display> ] f f 1/12 }
+        { [ <stack-track> ] f f 3/12 }
+        { [ <scrolling-pane> ] set-walker-track-pane [ <scroller> ] 1/2 }
+        { [ <walker-input> ] set-walker-track-input [ <scroller> ] 1/6 }
+    } { 0 1 } make-track* ;
+
+TUPLE: walker-gadget track ds rs cs quot ;
+
+: find-walker-gadget [ walker-gadget? ] find-parent ;
+
+: walker-gadget-pane walker-gadget-track walker-track-pane ;
+
+: walker-gadget-input walker-gadget-track walker-track-input ;
+
+: walker-command ( button word -- )
+    unit swap find-walker-gadget walker-gadget-input
+    interactor-call ;
+
+: <walker-toolbar> ( -- gadget )
+    {
+        { "Step" step }
+        { "Step in" into }
+        { "Step out" end-quot }
+        { "Step all" end }
+    } [
+        [
+            first2 [ walker-command ] curry <bevel-button> ,
+        ] each
+    ] make-toolbar ;
+
+: init-walker-models ( walker -- )
+    f <model> over set-walker-gadget-ds
+    f <model> over set-walker-gadget-rs
+    f <model> over set-walker-gadget-cs
+    f <model> swap set-walker-gadget-quot ;
+
+: walker-models ( -- cs rs ds quot )
+    gadget get walker-gadget-cs
+    gadget get walker-gadget-rs
+    gadget get walker-gadget-ds
+    gadget get walker-gadget-quot ;
+
+: walker-listener-hook ( walker -- )
+    meta-d get over walker-gadget-ds set-model
+    meta-r get over walker-gadget-rs set-model
+    meta-c get over walker-gadget-cs set-model
+    meta-callframe swap walker-gadget-quot set-model ;
+
+: walker-stream ( walker -- stream )
+    dup walker-gadget-input swap walker-gadget-pane
+    <duplex-stream> ;
+
+M: walker-gadget gadget-title
+    drop "Single stepper" <model> ;
+
+M: walker-gadget pref-dim*
+    delegate pref-dim* { 600 600 } vmax ;
+
+M: walker-gadget focusable-child* ( listener -- gadget )
+    walker-gadget-input ;
+
+: init-walker ( -- )
+    [ walker-listener-hook ] curry listener-hook set
+    "walk " listener-prompt set
+    continuation
+    V{ } clone over set-continuation-call
+    V{ } clone over set-continuation-data
+    set-meta-interp
+    [ ] (meta-call) ;
+
+: walker-thread ( walker -- )
+    [
+        init-namespaces
+        dup walker-stream [
+            [ init-walker clear ] listener
+        ] with-stream*
+    ] in-thread drop ;
+
+C: walker-gadget ( -- gadget )
+    dup init-walker-models {
+        { [ <walker-toolbar> ] f f @top }
+        { [ walker-models <walker-track> ] set-walker-gadget-track f @center }
+    } make-frame* dup walker-thread ;
+
+: (walk) ( quot walker -- )
+    >r [ meta-call ] curry r>
+    walker-gadget-input interactor-call ;
+
+: walker-tool
+    [ walker-gadget? ] [ <walker-gadget> ] [ (walk) ] ;
+
+: walk ( quot -- )
+    walker-tool call-tool ;