diff --git a/src/cg/01-stdlib.cg b/src/cg/01-stdlib.cg
index 9ba23ce..6a12a52 100644
--- a/src/cg/01-stdlib.cg
+++ b/src/cg/01-stdlib.cg
@@ -16,6 +16,15 @@ mapWithIndex = f list \
   f2 = acc x \ { i = acc.i + 1, result = [...acc.result, f x acc.i] };
   (fold f2 init list).result;
 
+# index : a \ List a \ Maybe Int
+index = x xs \
+  go = i rest \ rest
+    | [] \ None
+    | [y, ...ys] \ (x == y
+      | True \ Some i
+      | False \ go (i + 1) ys);
+  go 0 xs;
+
 # filter : (a \ Bool) \ List a \ List a
 filter = f list \ list
   | [] \ []
diff --git a/src/cg/10-os.cg b/src/cg/10-os.cg
index 5d5b33a..606859e 100644
--- a/src/cg/10-os.cg
+++ b/src/cg/10-os.cg
@@ -18,13 +18,25 @@ openWindow = title content \
     osState.palette.visible := False
   ];
 
-closeFocused = _ \
-  i = osState.wm.focusedIndex;
+closeWindowByIndex = i \
+  focused = osState.wm.focusedIndex;
+  newFocused = (i < focused
+    | True \ focused - 1
+    | False \ (i == focused
+      | True \ max 0 (focused - 1)
+      | False \ focused));
+
   batch [
     osState.windows := (take i osState.windows) & (drop (i + 1) osState.windows),
-    osState.wm.focusedIndex := max 0 (osState.wm.focusedIndex - 1)
+    osState.wm.focusedIndex := min newFocused (len osState.windows - 2)
   ];
 
+closeFocusedWindow = _ \ closeWindowByIndex osState.wm.focusedIndex;
+
+closeWindowById = id \
+  i = index id (map (w \ w.id) osState.windows);
+  closeWindowByIndex (unwrapOr 0 i);
+
 onSelect = input \
   result = eval input;
   result
@@ -33,7 +45,6 @@ onSelect = input \
   | Err msg \ openWindow "Error" (ui.text { content = msg, color = "red" });
 
 renderWindow = window isActive \
-  _ = debug "renderWindow" window.title;
   titleBarHeight = 30;
   ui.stack {
     children = [
@@ -45,8 +56,29 @@ renderWindow = window isActive \
         x = 0, y = 0,
         child = ui.stack {
           children = [
+            # background
             ui.rect { w = window.width, h = titleBarHeight, color = (isActive | True \ "#a15f80" | False \ "#0f3348") },
-            ui.positioned { x = 8, y = 8, child = ui.text { content = window.title, color = "white" } },
+            ui.row {
+              children = [
+                # close button
+                ui.clickable {
+                  event = closeWindowById window.id,
+                  child = ui.stack {
+                    children = [
+                      # button background
+                      ui.rect { w = titleBarHeight, h = titleBarHeight, color = "rgba(255,255,255,0.2)" },
+                      # button text
+                      ui.positioned {
+                        x = 9, y = 7, child = ui.text { content = "x" }
+                      }
+                    ]
+                  }
+                },
+
+                # title
+                ui.positioned { x = 8, y = 8, child = ui.text { content = window.title, color = "white" } },
+              ]
+            }
           ]
         }
       },
@@ -63,12 +95,23 @@ renderWindow = window isActive \
     ]
   };
 
+windowComponent = config \ ui.stateful {
+  key = "window-" & (show config.index),
+  focusable = True,
+  init = {},
+  update = state event \ event
+    | Focused \ { state = state, emit = [osState.wm.focusedIndex := config.index] }
+    | ChildFocused \ { state = state, emit = [osState.wm.focusedIndex := config.index] }
+    | _ \ { state = state, emit = [] },
+  view = state \ renderWindow config.window config.isActive
+};
+
 renderWindows = _ \
   windows = osState.windows;
   focused = osState.wm.focusedIndex;
   ui.row {
     gap = 1,
-    children = mapWithIndex (w i \ renderWindow w (i == focused)) windows
+    children = mapWithIndex (w i \ windowComponent { window = w, index = i, isActive = (i == focused) }) windows
   };
 
 os = ui.stateful {
@@ -85,8 +128,8 @@ os = ui.stateful {
     | Key { key = "ArrowRight", meta = True } \
       { state = state, emit = [osState.wm.focusedIndex := min (len osState.windows - 1) (osState.wm.focusedIndex + 1)] }
     | Key { key = "d", meta = True } \
-      { state = state, emit = [closeFocused 0] }
-    | _ \ _ = debug "key" []; { state = state, emit = [] },
+      { state = state, emit = [closeFocusedWindow 0] }
+    | _ \ { state = state, emit = [] },
 
   view = state \
     ui.stack {
diff --git a/src/compiler.ts b/src/compiler.ts
index dc7bc02..7ed3107 100644
--- a/src/compiler.ts
+++ b/src/compiler.ts
@@ -71,8 +71,8 @@ export function compile(ast: AST, useStore = true, bound = new Set<string>(), to
 
         case 'let':
             const newBound = new Set([...bound, ast.name]);
-            return `((${sanitizeName(ast.name)}) =>
-                     ${compile(ast.body, useStore, newBound, topLevel)})(${compile(ast.value, useStore, bound, topLevel)})`;
+            return `(() => { let ${sanitizeName(ast.name)} = ${compile(ast.value, useStore, newBound, topLevel)};
+                return ${compile(ast.body, useStore, newBound, topLevel)}; })()`;
 
         case 'match':
             return compileMatch(ast, useStore, bound, topLevel);
diff --git a/src/runtime-compiled.ts b/src/runtime-compiled.ts
index 7491402..fcde0f5 100644
--- a/src/runtime-compiled.ts
+++ b/src/runtime-compiled.ts
@@ -24,6 +24,7 @@ export function runAppCompiled(canvas: HTMLCanvasElement, store: any) {
 
     function setFocus(componentKey: string | null) {
         if (focusedComponentKey === componentKey) return;
+
         const oldFocus = focusedComponentKey;
         focusedComponentKey = componentKey;
 
@@ -36,6 +37,15 @@ export function runAppCompiled(canvas: HTMLCanvasElement, store: any) {
         if (componentKey && componentInstances.has(componentKey)) {
             handleComponentEvent(componentKey, { _tag: 'Focused' });
         }
+
+        // Notify ancestors
+        if (componentKey) {
+            for (const key of componentInstances.keys()) {
+                if (key !== componentKey && componentKey.startsWith(key + '.')) {
+                    handleComponentEvent(key, { _tag: 'ChildFocused' });
+                }
+            }
+        }
     }
 
     function handleComponentEvent(componentKey: string, event: any) {
diff --git a/src/ui.ts b/src/ui.ts
index 5867c85..eb2d370 100644
--- a/src/ui.ts
+++ b/src/ui.ts
@@ -88,8 +88,10 @@ function renderUI(ui: UIValue, ctx: CanvasRenderingContext2D, x: number, y: numb
         case 'row': {
             let offsetX = 0;
             for (const child of ui.children) {
+                const size = measure(child);
+                console.log("row child: ", child.kind, "width: ", size.width)
                 renderUI(child, ctx, x + offsetX, y);
-                offsetX += measure(child).width + ui.gap;
+                offsetX += measure(child).width + (ui.gap || 0);
             }
             break;
         }
@@ -98,7 +100,7 @@ function renderUI(ui: UIValue, ctx: CanvasRenderingContext2D, x: number, y: numb
             let offsetY = 0;
             for (const child of ui.children) {
                 renderUI(child, ctx, x, y + offsetY);
-                offsetY += measure(child).height + ui.gap;
+                offsetY += measure(child).height + (ui.gap || 0);
             }
             break;
         }
@@ -146,8 +148,16 @@ function renderUI(ui: UIValue, ctx: CanvasRenderingContext2D, x: number, y: numb
 }
 
 export function measure(ui: UIValue): { width: number, height: number } {
+    const result = _measure(ui);
+    if (isNaN(result.width) || isNaN(result.height)) {
+        console.warn('NaN from:', ui.kind, ui);
+    }
+    return result;
+}
+
+export function _measure(ui: UIValue): { width: number, height: number } {
     switch (ui.kind) {
-        case 'rect': return { width: ui.w, height: ui.h };
+        case 'rect': return { width: ui.w || 0, height: ui.h || 0 };
 
         case 'text': return { width: ui.content.length * 10, height: 20 }; // TODO
 
@@ -159,7 +169,7 @@ export function measure(ui: UIValue): { width: number, height: number } {
                 totalWidth += size.width;
                 maxHeight = Math.max(maxHeight, size.height);
             }
-            totalWidth += ui.gap * (ui.children.length - 1);
+            totalWidth += (ui.gap || 0) * (ui.children.length - 1);
             return { width: totalWidth, height: maxHeight };
         }
 
@@ -171,7 +181,7 @@ export function measure(ui: UIValue): { width: number, height: number } {
                 totalHeight += size.height;
                 maxWidth = Math.max(maxWidth, size.width);
             }
-            totalHeight += ui.gap * (ui.children.length - 1);
+            totalHeight += (ui.gap || 0) * (ui.children.length - 1);
             return { width: maxWidth, height: totalHeight };
         }
 
@@ -209,6 +219,8 @@ export function measure(ui: UIValue): { width: number, height: number } {
 
         case 'stateful':
             throw new Error('Stateful components cannot be measured');
+
+        default: return { width: 0, height: 0 };
     }
 }