diff --git a/src/cg/03-ui-components.cg b/src/cg/03-ui-components.cg
index 174d732..47286c2 100644
--- a/src/cg/03-ui-components.cg
+++ b/src/cg/03-ui-components.cg
@@ -210,7 +210,7 @@ textInput = config \
       # | Key { key = k } \ { state = state, emit = [\ c.onKeyDown k ] }
       | _ \ { state = state, emit = [] },
 
-    view = state \
+    view = state emit \
       textBeforeCursor = slice state.text 0 state.cursorPos;
       cursorX = ui.measureText textBeforeCursor;
       padding = 8;
diff --git a/src/cg/05-palette.cg b/src/cg/05-palette.cg
index 14ce888..c558ad9 100644
--- a/src/cg/05-palette.cg
+++ b/src/cg/05-palette.cg
@@ -99,7 +99,7 @@ palette = config \
         | _ \ { state = state, emit = [] })
       | _ \ { state = state, emit = [] },
 
-    view = state \
+    view = state emit \
       ui.positioned {
         x = (config.viewport.width - windowWidth) / 2,
         y = (config.viewport.height - windowHeight) / 2,
diff --git a/src/cg/06-inspector.cg b/src/cg/06-inspector.cg
index f394147..6bda7ee 100644
--- a/src/cg/06-inspector.cg
+++ b/src/cg/06-inspector.cg
@@ -1,11 +1,4 @@
 inspector = config \
-  windowHeight = 400;
-  windowWidth = 600;
-
-  source = getSource config.name;
-  sourceLines = split "\n" source;
-  lineHeight = 20;
-
   val = eval config.name;
   _ = debug "val" val;
 
@@ -13,36 +6,17 @@ inspector = config \
     | Value v \ reflect v
     | _ \ reflect 0;
 
-  _ = debug "reflected" reflected;
-
-  dialogPadding = 0;
-
   textInputHeight = 40;
-  contentWidth = windowWidth - (dialogPadding * 2);
-  contentHeight = windowHeight - (dialogPadding * 2);
 
   ui.column {
     gap = 0,
     children = [
-      # display source
-      scrollable {
+      # tree
+      tree {
+        value = reflected,
+        path = config.name,
         w = config.w,
-        h = config.h - textInputHeight,
-        totalWidth = config.w,
-        # totalHeight = (len sourceLines) * lineHeight,
-        totalHeight = 1000,
-        onScroll = _ \ noOp,
-        child = tree { value = reflected, depth = 0, path = config.name },
-        # child = ui.column {
-        #   gap = 0,
-        #   children = map (line \
-        #     ui.positioned {
-        #       x = 8,
-        #       y = 2,
-        #       child = ui.text { content = line, color = "#ccc" }
-        #     }
-        #   ) sourceLines
-        # }
+        h = config.h - textInputHeight
       },
 
       # definition bar
diff --git a/src/cg/06-tree.cg b/src/cg/06-tree.cg
index f097634..e0523a0 100644
--- a/src/cg/06-tree.cg
+++ b/src/cg/06-tree.cg
@@ -1,4 +1,32 @@
-tree = config \
+treeNodeHeight = value path expanded \
+  lineH = 20;
+  valueLabel = v \ v
+  | NumberValue n \ Some n
+  | StringValue n \ Some n
+  | ConstructorValue { tag = tag } \ Some tag
+  | FunctionValue _ \ Some "<fn>"
+  | _ \ None;
+
+  value
+  | RecordValue entries \
+    (contains path expanded)
+    | True \ lineH + (sum (map (entry \
+        (valueLabel entry.value)
+        | Some _ \ lineH
+        | None \ lineH + (treeNodeHeight entry.value (path & "." & entry.key) expanded)
+      ) entries))
+    | False \ lineH
+  | ListValue items \
+    (contains path expanded)
+    | True \ lineH + (sum (mapWithIndex (item i \
+        (valueLabel item)
+        | Some _ \ lineH
+        | None \ lineH + (treeNodeHeight item (path & "." & (show i)) expanded)
+      ) items))
+    | False \ lineH
+  | _ \ lineH;
+
+treeNode = config \
   depth = config.depth;
   indent = depth * 20;
 
@@ -14,51 +42,76 @@ tree = config \
     | FunctionValue _ \ Some "<fn>"
     | _ \ None;
 
+  header = isExp label color \
+    ui.clickable {
+      onClick = _ \ config.onToggle config.path,
+      child = simple ((isExp | True \ "▼ " | False \ "▶ ") & label) color
+    };
+
+  isExp = contains config.path config.expanded;
+
   config.value
   | NumberValue n \ simple (show n) "#6cf"
   | StringValue n \ simple ("\"" & n & "\"") "#f6a"
   | ConstructorValue { tag = tag } \ simple tag "#fc6"
   | FunctionValue _ \ simple "<fn>" "#888"
   | RecordValue entries \
-    ui.stateful {
-      key = "tree-" & config.path,
-      init = { collapsed = True },
-
-      update = state event \ event
-        | Clicked _ \ (
-        _ = debug "clicked on node" [];
-        { state = state.{ collapsed = (not state.collapsed) }, emit = [] }
-        )
-        | _ \ { state = state, emit = [] },
-
-      view = state \
-        ui.column {
-          gap = 0,
-          children = [
-            simple ((state.collapsed | True \ "▶ " | False \ "▼ ") & (show (len entries)) & " fields") "#888",
-            ...(state.collapsed
-              | True \ []
-              | False \ map (entry \
-                (valueLabel entry.value)
-                | Some label \ simple (entry.key & " = " & label) "#aaa"
-                | None \ ui.column { gap = 0, children = [
-                    simple entry.key "#aaa",
-                    tree { value = entry.value, depth = depth + 1, path = config.path & "." & entry.key }
-                  ]}
-              ) entries)
-          ]
-        }
-    }
+    ui.column { gap = 0, children = [
+      header isExp ((show (len entries)) & " fields") "#888",
+      ...(isExp
+        | True \ [ui.clickable {
+          onClick = _ \ noOp,
+          child = ui.column { gap = 0, children = map (entry \
+              (valueLabel entry.value)
+              | Some label \ simple (entry.key & " = " & label) "#aaa"
+              | None \ ui.column { gap = 0, children = [
+                  simple entry.key "#aaa",
+                  treeNode { value = entry.value, depth = depth + 1, path = config.path & "." & entry.key, expanded = config.expanded, onToggle = config.onToggle }
+                ]}
+            ) entries }
+        }]
+        | False \ [])
+    ]}
   | ListValue items \
-    ui.column {
-      gap = 0,
-      children = mapWithIndex (item i \
-        (valueLabel item)
-        | Some label \ simple ((show i) & ": " & label) "#aaa"
-        | None \ ui.column { gap = 0, children = [
-            simple (show i) "#aaa",
-            tree { value = item, depth = depth + 1 }
-          ]}
-      ) items
-    }
+    ui.column { gap = 0, children = [
+      header isExp ((show (len items)) & " items") "#888",
+      ...(isExp
+        | True \ [ui.clickable {
+          onClick = _ \ noOp,
+          child = ui.column { gap = 0, children = mapWithIndex (item i \
+              (valueLabel item)
+              | Some label \ simple ((show i) & " : " & label) "#aaa"
+              | None \ ui.column { gap = 0, children = [
+                  simple (show i) "#aaa",
+                  treeNode { value = item, depth = depth + 1, path = config.path & "." & (show i), expanded = config.expanded, onToggle = config.onToggle }
+                ]}
+            ) items }
+        }]
+        | False \ [])
+    ]}
   | _ \ ui.text { content = "?", color = "#666" };
+
+tree = config \
+  ui.stateful {
+    key = "tree-" & config.path,
+    init = { expanded = [] },
+
+    update = state event \ event
+      | Toggle path \ ((contains path state.expanded)
+        | True \ { state = state.{ expanded = filter (p \ p != path) state.expanded }, emit = [] }
+        | False \ { state = state.{ expanded = [path, ...state.expanded] }, emit = [] })
+      | _ \ { state = state, emit = [] },
+
+    view = state emit \
+      onToggle = path \ emit (Toggle path);
+      totalH = treeNodeHeight config.value config.path state.expanded;
+
+      scrollable {
+        w = config.w,
+        h = config.h,
+        totalWidth = config.w,
+        totalHeight = totalH,
+        onScroll = _ \ noOp,
+        child = treeNode { value = config.value, path = config.path, depth = 0, expanded = state.expanded, onToggle = onToggle }
+      }
+  };
diff --git a/src/cg/10-os.cg b/src/cg/10-os.cg
index 5b0d70a..8a59700 100644
--- a/src/cg/10-os.cg
+++ b/src/cg/10-os.cg
@@ -137,7 +137,7 @@ os =
       | Focused \ { state = state, emit = [focusWindow config.index] }
       | ChildFocused \ { state = state, emit = [focusWindow config.index] }
       | _ \ { state = state, emit = [] },
-    view = state \ renderWindow config.window config.isActive
+    view = state emit \ renderWindow config.window config.isActive
   };
 
   renderWindows = _ \
@@ -203,7 +203,7 @@ os =
         { state = state, emit = [toggleMaximizeFocusedWindow 0] }
       | _ \ { state = state, emit = [] },
 
-    view = state \
+    view = state emit \
       ui.stack {
         children = [
           ui.rect { w = viewport.width, h = viewport.height, color = "#012" },
diff --git a/src/runtime-compiled.ts b/src/runtime-compiled.ts
index d9c263d..de72d0b 100644
--- a/src/runtime-compiled.ts
+++ b/src/runtime-compiled.ts
@@ -92,7 +92,9 @@ export function runAppCompiled(canvas: HTMLCanvasElement, store: any) {
                     setFocus(fullKey);
                 }
 
-                const viewResult = instance.view(instance.state);
+                const emit = (event: any) => ({ _tag: 'ComponentEvent', _0: fullKey, _1: event });
+                const viewResult = instance.view(instance.state)(emit);
+
                 const viewUI = {
                     kind: 'clickable',
                     child: viewResult,
@@ -206,6 +208,11 @@ export function runAppCompiled(canvas: HTMLCanvasElement, store: any) {
             return;
         }
 
+        if (event._tag === 'ComponentEvent') {
+            handleComponentEvent(event._0, event._1);
+            return;
+        }
+
         if (event._tag === 'NoOp')
             return;
     }