diff --git a/build.sh b/build.sh
index b0662ea..572d280 100755
--- a/build.sh
+++ b/build.sh
@@ -1,6 +1,6 @@
 #!/bin/bash
 
-mkdir -p bin && javac -d bin snippets/*.java
+rm -rf bin && mkdir -p bin && javac --enable-preview --source 22 -d bin snippets/*.java
 
 marp slides.md -o slides.html
 marp slides.md -o slides.pdf
diff --git a/snippets/Either.java b/snippets/Either.java
index bae7adc..a9ec373 100644
--- a/snippets/Either.java
+++ b/snippets/Either.java
@@ -1,5 +1,3 @@
-package snippets;
-
 import java.util.function.Function;
 
 sealed interface Either<L, R> {
diff --git a/snippets/Expr.java b/snippets/Expr.java
index 55e6529..0321856 100644
--- a/snippets/Expr.java
+++ b/snippets/Expr.java
@@ -1,5 +1,3 @@
-package snippets;
-
 sealed interface Expr {
 
     record Lit(int value) implements Expr {}
@@ -41,8 +39,8 @@
         return new Times(left, right);
     }
 
-    static void run() {
-        sum(lit(1), lit(2)).evaluate(); // 3
-        sum(diff(lit(10), lit(8)), lit(2)).evaluate(); // 4
+    static void main() {
+        assert sum(lit(1), lit(2)).evaluate() == 3; // 1 + 2 = 3
+        assert times(diff(lit(10), lit(8)), lit(2)).evaluate() == 4; // (10 - 8) * 2 = 4
     }
 }
diff --git a/snippets/Json.java b/snippets/Json.java
index dad806d..bd48bbc 100644
--- a/snippets/Json.java
+++ b/snippets/Json.java
@@ -1,5 +1,3 @@
-package snippets;
-
 import java.util.List;
 import java.util.Map;
 
diff --git a/snippets/List.java b/snippets/List.java
index ee122db..5200b03 100644
--- a/snippets/List.java
+++ b/snippets/List.java
@@ -1,5 +1,3 @@
-package snippets;
-
 import java.util.function.Function;
 import java.util.function.Predicate;
 
diff --git a/snippets/Movie.java b/snippets/Movie.java
index 1826a5d..817989e 100644
--- a/snippets/Movie.java
+++ b/snippets/Movie.java
@@ -1,5 +1,3 @@
-package snippets;
-
 public record Movie(String title, int year, int duration) {
 
     public Movie {
diff --git a/snippets/MovieRepository.java b/snippets/MovieRepository.java
index dd99244..16ba674 100644
--- a/snippets/MovieRepository.java
+++ b/snippets/MovieRepository.java
@@ -1,5 +1,3 @@
-package snippets;
-
 interface MovieRepository {
     MovieResponse create(Movie movie);
 }
diff --git a/snippets/MovieResponse.java b/snippets/MovieResponse.java
index f8c0b6c..ec2b9d8 100644
--- a/snippets/MovieResponse.java
+++ b/snippets/MovieResponse.java
@@ -1,5 +1,3 @@
-package snippets;
-
 import java.util.UUID;
 
 sealed interface MovieResponse {
diff --git a/snippets/Optional.java b/snippets/Optional.java
index 4cf3d4a..f5c7b4c 100644
--- a/snippets/Optional.java
+++ b/snippets/Optional.java
@@ -1,5 +1,3 @@
-package snippets;
-
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.function.Supplier;
diff --git a/snippets/Shape.java b/snippets/Shape.java
index be837a7..5170727 100644
--- a/snippets/Shape.java
+++ b/snippets/Shape.java
@@ -1,5 +1,3 @@
-package snippets;
-
 sealed interface Shape {
 
     record Square(int side) implements Shape {}
diff --git a/snippets/Switches.java b/snippets/Switches.java
index c4e9988..066373d 100644
--- a/snippets/Switches.java
+++ b/snippets/Switches.java
@@ -1,5 +1,3 @@
-package snippets;
-
 class Switches {
 
     void method1(String input) {
diff --git a/snippets/Tree.java b/snippets/Tree.java
index d5fd876..a3ec82a 100644
--- a/snippets/Tree.java
+++ b/snippets/Tree.java
@@ -1,5 +1,3 @@
-package snippets;
-
 sealed interface Tree<T> {
     record Node<T>(T value, Tree<T> left, Tree<T> right) implements Tree<T> { }
     record Leaf<T>(T value) implements Tree<T> {}