diff --git a/lynglib/stdlib/lyng/root.lyng b/lynglib/stdlib/lyng/root.lyng
index 01c72a7..644857a 100644
--- a/lynglib/stdlib/lyng/root.lyng
+++ b/lynglib/stdlib/lyng/root.lyng
@@ -22,6 +22,23 @@ extern class Iterator<T> {
     fun toList(): List<T>
 }
 
+extern class Collection<T> : Iterable<T> {
+}
+
+extern class Array<T> : Collection<T> {
+}
+
+extern class List<T> : Array<T> {
+}
+
+extern class Set<T> : Collection<T> {
+}
+
+extern class Map<K,V> {
+}
+
+extern class MapEntry<K,V>
+
 // Built-in math helpers (implemented in host runtime).
 extern fun abs(x: Object): Real
 extern fun ln(x: Object): Real