diff --git a/src/ast.ts b/src/ast.ts
index b42906b..0b8bf41 100644
--- a/src/ast.ts
+++ b/src/ast.ts
@@ -147,6 +147,7 @@ export type Definition = {
     column?: number
     start?: number
     annotation?: Annotation
+    module?: string
 }
 
 export type Rebind = {
@@ -175,6 +176,7 @@ export type TypeDefinition = {
     line?: number
     column?: number
     start?: number
+    module?: string
 }
 
 export type Annotation = {
@@ -195,6 +197,7 @@ export type ClassDefinition = {
     line?: number
     column?: number
     start?: number
+    module?: string
 }
 
 export type InstanceDeclaration = {
@@ -204,6 +207,7 @@ export type InstanceDeclaration = {
     line?: number
     column?: number
     start?: number
+    module?: string
 }
 
 export type AST =
diff --git a/src/cg/03-ui-components.cg b/src/cg/03-ui-components.cg
index ac64bef..9e46167 100644
--- a/src/cg/03-ui-components.cg
+++ b/src/cg/03-ui-components.cg
@@ -390,60 +390,62 @@ LayoutChild = Fixed Int (Int \ Int \ UI) | Flex Int (Int \ Int \ UI);
 Alignment = Start | Center | End;
 Direction = Col | Row;
 
-layout = {
-  layoutDir
-    # : Direction \ { w : Int, h : Int } \ List LayoutChild \ { ui : UI, w : Int, h : Int }
-    = dir constraints children \
-    mainSize = dir | Col \ constraints.h | Row \ constraints.w;
-    crossSize = dir | Col \ constraints.w | Row \ constraints.h;
+@layout
 
-    # Pass 1: sum fixed heights, total flex weight
-    info = fold (acc child \ child
-      | Fixed s _ \ acc.{ fixedMain = acc.fixedMain + s }
-      | Flex n _ \ acc.{ totalFlex = acc.totalFlex + n }
-     ) { fixedMain = 0, totalFlex = 0 } children;
+layoutDir
+  : Direction \ { w : Int, h : Int } \ List LayoutChild \ { ui : UI, w : Int, h : Int }
+  = dir constraints children \
+  mainSize = dir | Col \ constraints.h | Row \ constraints.w;
+  crossSize = dir | Col \ constraints.w | Row \ constraints.h;
 
-     remaining = mainSize - info.fixedMain;
+  # Pass 1: sum fixed heights, total flex weight
+  info = fold (acc child \ child
+    | Fixed s _ \ acc.{ fixedMain = acc.fixedMain + s }
+    | Flex n _ \ acc.{ totalFlex = acc.totalFlex + n }
+   ) { fixedMain = 0, totalFlex = 0 } children;
 
-     # Pass 2
-     result = fold (acc child \
-       allocated = (child
-         | Fixed s view \ { s = s, view = view }
-         | Flex n view \ { s = remaining * n / info.totalFlex, view = view });
+   remaining = mainSize - info.fixedMain;
 
-        childW = dir | Col \ crossSize | Row \ allocated.s;
-        childH = dir | Col \ allocated.s | Row \ crossSize;
-        posX = dir | Col \ 0 | Row \ acc.pos;
-        posY = dir | Col \ acc.pos | Row \ 0;
+   # Pass 2
+   result = fold (acc child \
+     allocated = (child
+       | Fixed s view \ { s = s, view = view }
+       | Flex n view \ { s = remaining * n / info.totalFlex, view = view });
 
-        rendered = ui.positioned {
-          x = posX, y = posY,
-          child = allocated.view childW childH
-        };
+      childW = dir | Col \ crossSize | Row \ allocated.s;
+      childH = dir | Col \ allocated.s | Row \ crossSize;
+      posX = dir | Col \ 0 | Row \ acc.pos;
+      posY = dir | Col \ acc.pos | Row \ 0;
 
-      acc.{ pos = acc.pos + allocated.s, children = [...acc.children, rendered] }
-    ) { pos = 0, children = [] } children;
+      rendered = ui.positioned {
+        x = posX, y = posY,
+        child = allocated.view childW childH
+      };
 
-    { ui = ui.stack { children = result.children }, w = constraints.w, h = constraints.h },
+    acc.{ pos = acc.pos + allocated.s, children = [...acc.children, rendered] }
+  ) { pos = 0, children = [] } children;
 
-  col = layoutDir Col,
-  row = layoutDir Row,
+  { ui = ui.stack { children = result.children }, w = constraints.w, h = constraints.h };
 
-  align = hAlign vAlign w h child \
-    x = hAlign
-      | Start \ 0
-      | Center \ (w - child.w) / 2
-      | End \ w - child.w;
-    y = vAlign
-      | Start \ 0
-      | Center \ (h - child.h) / 2
-      | End \ h - child.h;
-    { ui = ui.positioned { x = x, y = y, child = child.ui }, w = w, h = h },
-};
+col = layoutDir Col;
+row = layoutDir Row;
+
+align = hAlign vAlign w h child \
+  x = hAlign
+    | Start \ 0
+    | Center \ (w - child.w) / 2
+    | End \ w - child.w;
+  y = vAlign
+    | Start \ 0
+    | Center \ (h - child.h) / 2
+    | End \ h - child.h;
+  { ui = ui.positioned { x = x, y = y, child = child.ui }, w = w, h = h };
+
+@
 
 testApp = name \
   { view = ctx \
-    layout.col { w = ctx.w, h = ctx.h } [
+    col { w = ctx.w, h = ctx.h } [
       Fixed 40 (w h \ box { w = w, h = h, color = "red", child = text "Header" }),
       Flex 1 (w h \ box { w = w, h = h, color = "#1a1a2e", child = text "Main content" }),
       Fixed 30 (w h \ box { w = w, h = h, color = "blue", child = text "Footer" }),
@@ -453,13 +455,13 @@ testApp = name \
 
 testApp2 = _ \
   { view = ctx \
-    layout.col { w = ctx.w, h = ctx.h } [
-      Fixed 40 (w h \ (layout.align Center Center w h (sizedText "Header")).ui),
-      Flex 1 (w h \ (layout.row { w = w, h = h } [
+    col { w = ctx.w, h = ctx.h } [
+      Fixed 40 (w h \ (align Center Center w h (sizedText "Header")).ui),
+      Flex 1 (w h \ (row { w = w, h = h } [
         Fixed 200 (w h \ box { w = w, h = h, color = "#2a2a3e", child = text "Sidebar" }),
         Flex 1 (w h \ box { w = w, h = h, color = "#1a1a2e", child = text "Main" }),
       ]).ui),
-      Fixed 30 (w h \ (layout.align Center Center w h (sizedText "Footer")).ui),
+      Fixed 30 (w h \ (align Center Center w h (sizedText "Footer")).ui),
     ]
     ~ (e \ e.ui)
   };
diff --git a/src/parser.ts b/src/parser.ts
index 5b258b8..b804b3f 100644
--- a/src/parser.ts
+++ b/src/parser.ts
@@ -150,6 +150,8 @@ export class Parser {
         }
     }
 
+    private currentModule: string | undefined;
+
     parse(): { definitions: Definition[], typeDefinitions: TypeDefinition[], classDefinitions: ClassDefinition[], instanceDeclarations: InstanceDeclaration[] } {
         const definitions: Definition[] = [];
         const typeDefinitions: TypeDefinition[] = [];
@@ -157,22 +159,41 @@ export class Parser {
         const instanceDeclarations: InstanceDeclaration[] = [];
 
         while (this.current().kind !== 'eof') {
+            // Module tags
+            if (this.current().kind === 'at') {
+                this.advance();
+                if (this.current().kind === 'ident' && this.peek().kind !== 'equals' && this.peek().kind !== 'colon') {
+                    this.currentModule = (this.advance() as { value: string }).value;
+                } else {
+                    this.currentModule = undefined;
+                }
+                continue;
+            }
+
             if (this.current().kind === 'type-ident') {
                 let offset = 1;
                 while (this.peek(offset).kind === 'ident') offset++;
                 const after = this.peek(offset);
 
                 if (after.kind === 'open-brace') {
-                    classDefinitions.push(this.parseClassDefinition());
+                    const cd = this.parseClassDefinition();
+                    if (this.currentModule) cd.module = this.currentModule;
+                    classDefinitions.push(cd);
                 } else if (after.kind === 'colon') {
-                    instanceDeclarations.push(this.parseInstanceDeclaration());
+                    const id = this.parseInstanceDeclaration();
+                    if (this.currentModule) id.module = this.currentModule;
+                    instanceDeclarations.push(id);
                 } else {
-                    typeDefinitions.push(this.parseTypeDefinition());
+                    const td = this.parseTypeDefinition();
+                    if (this.currentModule) td.module = this.currentModule;
+                    typeDefinitions.push(td);
                 }
                 continue;
             }
 
-            definitions.push(this.parseDefinition());
+            const def = this.parseDefinition();
+            if (this.currentModule) def.module = this.currentModule;
+            definitions.push(def);
         }
 
         return { definitions, typeDefinitions, classDefinitions, instanceDeclarations };