diff --git a/slides.md b/slides.md
index 20fe91a..8dccaa0 100644
--- a/slides.md
+++ b/slides.md
@@ -500,6 +500,85 @@
 
 ---
 
+# ADTs: DSLs
+
+```java
+sealed interface Expr {
+    record Val(int value) implements Expr {}
+    record Sum(Expr left, Expr right) implements Expr {}
+    record Diff(Expr left, Expr right) implements Expr {}
+    record Times(Expr left, Expr right) implements Expr {}
+}
+```
+
+* ADTs son muy útiles para definir DSLs
+
+---
+
+# ADTs: DSLs
+
+```java
+sealed interface Expr {
+    default int evaluate() {
+        return switch (this) {
+            case Val(var value) -> value;
+            case Sum(var left, var right) -> left.evaluate() + right.evaluate();
+            case Diff(var left, var right) -> left.evaluate() - right.evaluate();
+            case Times(var left, var right) -> left.evaluate() * right.evaluate();
+        };
+    }
+}
+```
+
+---
+
+# ADTs: DSLs
+
+```java
+sealed interface Expr {
+    default String asString() {
+        return switch (this) {
+            case Val(var value) -> String.valueOf(value);
+            case Sum(var left, var right) -> "(" + left.asString() + "+" + right.asString() + ")";
+            case Diff(var left, var right) -> "(" + left.asString() + "-" + right.asString() + ")";
+            case Times(var left, var right) -> "(" + left.asString() + "*" + right.asString() + ")";
+        };
+    }
+}
+```
+
+---
+
+# ADTs: DSLs
+
+```java
+sealed interface Expr {
+    default void print() {
+        System.out.println(asString() + "=" + evaluate());
+    }
+}
+```
+
+---
+
+# ADTs: DSLs
+
+```java
+sealed interface Expr {
+    static void main() {
+        sum(val(1), val(2)).print();
+        times(diff(val(10), val(8)), val(2)).print();
+    }
+}
+```
+
+```
+(1+2)=3
+((10-8)*2)=4
+```
+
+---
+
 # ADTs: Errores
 
 ```java
@@ -530,6 +609,40 @@
 ```
 
 ---
+# ADTs: Errores
+
+```java
+@PostMapping("/movies")
+public ResponseEntity<Integer> create(@RequestBody Movie movie) {
+    var result = repository.create(movie);
+    return switch (result) {
+        case MovieCreated(var id) -> ResponseEntity.ok(id);
+        case MovieError e -> ResponseEntity.of(toProblem(e)).build();
+    };
+}
+```
+
+---
+# ADTs: Errores
+
+```java
+static ProblemDetail toProblem(CreateMovieResponse.MovieError error) {
+    var detail = switch (error) {
+      case DuplicatedMovie(int id) -> "duplicated movie with id: " + id;
+      case InvalidDuration(var duration) -> "invalid duration: " + duration;
+      case InvalidYear(var duration) -> "invalid year: " + duration;
+      case InvalidStars(var stars) -> "invalid stars: " + stars;
+      case EmptyTitle() -> "title cannot be empty";
+      case EmptyDirector() -> "director cannot be empty";
+      case EmptyCast() -> "cast cannot be empty";
+      case DuplicatedActor(var actor) -> "duplicated actor: " + actor;
+    };
+
+    return ProblemDetail.forStatusAndDetail(BAD_REQUEST, detail);
+}
+```
+
+---
 
 # ADTs: Either
 
@@ -539,6 +652,16 @@
 }
 ```
 
+```java
+@PostMapping("/movies")
+public ResponseEntity<Integer> create(@RequestBody Movie movie) {
+    var result = repository.create(movie);
+    return result.fold(
+        error -> ResponseEntity.of(toProblem(error)).build(),
+        ResponseEntity::ok);
+}
+```
+
 ---
 
 # Próximamente :watch:
diff --git a/snippets/Expr.java b/snippets/Expr.java
index 0321856..0b9aabe 100644
--- a/snippets/Expr.java
+++ b/snippets/Expr.java
@@ -1,30 +1,34 @@
 sealed interface Expr {
 
-    record Lit(int value) implements Expr {}
+    record Val(int value) implements Expr {}
     record Sum(Expr left, Expr right) implements Expr {}
     record Diff(Expr left, Expr right) implements Expr {}
     record Times(Expr left, Expr right) implements Expr {}
 
     default int evaluate() {
         return switch (this) {
-            case Lit(var value) -> value;
+            case Val(var value) -> value;
             case Sum(var left, var right) -> left.evaluate() + right.evaluate();
             case Diff(var left, var right) -> left.evaluate() - right.evaluate();
             case Times(var left, var right) -> left.evaluate() * right.evaluate();
         };
     }
-      
-    default String print() {
+
+    default String asString() {
         return switch (this) {
-            case Lit(var value) -> String.valueOf(value);
-            case Sum(var left, var right) -> "(" + left.print() + "+" + right.print() + ")";
-            case Diff(var left, var right) -> "(" + left.print() + "-" + right.print() + ")";
-            case Times(var left, var right) -> "(" + left.print() + "*" + right.print() + ")";
+            case Val(var value) -> String.valueOf(value);
+            case Sum(var left, var right) -> "(" + left.asString() + "+" + right.asString() + ")";
+            case Diff(var left, var right) -> "(" + left.asString() + "-" + right.asString() + ")";
+            case Times(var left, var right) -> "(" + left.asString() + "*" + right.asString() + ")";
         };
     }
 
-    static Expr lit(int value) {
-        return new Lit(value);
+    default void print() {
+        System.out.println(asString() + "=" + evaluate());
+    }
+
+    static Expr val(int value) {
+        return new Val(value);
     }
 
     static Expr sum(Expr left, Expr right) {
@@ -40,7 +44,7 @@
     }
 
     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
+        sum(val(1), val(2)).print();
+        times(diff(val(10), val(8)), val(2)).print();
     }
 }