diff --git a/README.md b/README.md
index 33e1d9a..e027f01 100644
--- a/README.md
+++ b/README.md
@@ -6,3 +6,4 @@ Making a lambda calculus interpreter in Go.
 
 - Exhaustive sum types.
 - Recursive descent and left-recursion.
+- Observer pattern, event emission.