diff --git a/graalpy/graalpy-micronaut-pygal-charts/README.md b/graalpy/graalpy-micronaut-pygal-charts/README.md
index d69d788..aa26d4b 100644
--- a/graalpy/graalpy-micronaut-pygal-charts/README.md
+++ b/graalpy/graalpy-micronaut-pygal-charts/README.md
@@ -20,7 +20,7 @@ To start the demo, simply run:
 ./mvnw package mn:run
 ```
 
-When the demo runs, open the follwing URLs in a browser:
+When the demo runs, open the following URLs in a browser:
 
 | URL                           | Service                       |
 |:------------------------------|:------------------------------|
diff --git a/graalpy/graalpy-micronaut-pygal-charts/src/main/java/com/example/PyGalServiceMixed.java b/graalpy/graalpy-micronaut-pygal-charts/src/main/java/com/example/PyGalServiceMixed.java
index f93fc7e..8061f44 100644
--- a/graalpy/graalpy-micronaut-pygal-charts/src/main/java/com/example/PyGalServiceMixed.java
+++ b/graalpy/graalpy-micronaut-pygal-charts/src/main/java/com/example/PyGalServiceMixed.java
@@ -7,17 +7,16 @@
 package com.example;
 
 import jakarta.inject.Singleton;
-import org.graalvm.polyglot.Value;
 
 import java.util.List;
 import java.util.stream.IntStream;
 
 @Singleton
 public class PyGalServiceMixed implements PyGalService {
-    private final Value pythonFunctionXY;
+    private final RenderXYFunction renderXYFunction;
 
     PyGalServiceMixed(GraalPyContext graalPyContext) {
-        pythonFunctionXY = graalPyContext.eval(
+        renderXYFunction = graalPyContext.eval(
                 // language=python
                 """
                         import pygal
@@ -29,12 +28,17 @@ def render_xy(title, label_datapoint_entries):
                                 xy_chart.add(entry.label(), entry.dataPoints())
                             return xy_chart.render().decode()
                         
-                        render_xy""");
+                        render_xy""").as(RenderXYFunction.class);
     }
 
     public record Entry(String label, double[][] dataPoints) {
     }
 
+    @FunctionalInterface
+    public interface RenderXYFunction {
+        String apply(String title, List<Entry> labelDatapointEntries);
+    }
+
     @Override
     public String renderXYChart() {
         String title = "XY Cosinus";
@@ -46,6 +50,6 @@ public String renderXYChart() {
                 new Entry("y = 1", new double[][]{{-5, 1}, {5, 1}}),
                 new Entry("y = -1", new double[][]{{-5, -1}, {5, -1}})
         );
-        return pythonFunctionXY.execute(title, labelDatapointEntries).asString();
+        return renderXYFunction.apply(title, labelDatapointEntries);
     }
 }
diff --git a/graalpy/graalpy-micronaut-pygal-charts/src/main/resources/META-INF/native-image/com.example/demo/reachability-metadata.json b/graalpy/graalpy-micronaut-pygal-charts/src/main/resources/META-INF/native-image/com.example/demo/reachability-metadata.json
index 56b5111..92d4ee3 100644
--- a/graalpy/graalpy-micronaut-pygal-charts/src/main/resources/META-INF/native-image/com.example/demo/reachability-metadata.json
+++ b/graalpy/graalpy-micronaut-pygal-charts/src/main/resources/META-INF/native-image/com.example/demo/reachability-metadata.json
@@ -3,6 +3,9 @@
     {
       "type": "com.example.PyGalServiceMixed$Entry"
     },
+    {
+      "type": "com.example.PyGalServiceMixed$RenderXYFunction"
+    },
     {
       "type": "com.example.PyGalServicePureJava$BytesIO"
     },
@@ -12,6 +15,13 @@
     {
       "type": "com.example.PyGalServicePureJava$XY"
     },
+    {
+      "type": {
+        "proxy": [
+          "com.example.PyGalServiceMixed$RenderXYFunction"
+        ]
+      }
+    },
     {
       "type": {
         "proxy": [
diff --git a/graalpy/graalpy-spring-boot-pygal-charts/README.md b/graalpy/graalpy-spring-boot-pygal-charts/README.md
index 349381e..e3b5332 100644
--- a/graalpy/graalpy-spring-boot-pygal-charts/README.md
+++ b/graalpy/graalpy-spring-boot-pygal-charts/README.md
@@ -20,7 +20,7 @@ To start the demo, simply run:
 ./mvnw package spring-boot:run
 ```
 
-When the demo runs, open the follwing URLs in a browser:
+When the demo runs, open the following URLs in a browser:
 
 | URL                           | Service                       |
 |:------------------------------|:------------------------------|
diff --git a/graalpy/graalpy-spring-boot-pygal-charts/src/main/java/com/example/demo/PyGalServiceMixed.java b/graalpy/graalpy-spring-boot-pygal-charts/src/main/java/com/example/demo/PyGalServiceMixed.java
index f0fc98b..365c9de 100644
--- a/graalpy/graalpy-spring-boot-pygal-charts/src/main/java/com/example/demo/PyGalServiceMixed.java
+++ b/graalpy/graalpy-spring-boot-pygal-charts/src/main/java/com/example/demo/PyGalServiceMixed.java
@@ -7,7 +7,6 @@
 package com.example.demo;
 
 import com.example.demo.GraalPyContextConfiguration.GraalPyContext;
-import org.graalvm.polyglot.Value;
 import org.springframework.stereotype.Service;
 
 import java.util.List;
@@ -15,10 +14,10 @@
 
 @Service
 public class PyGalServiceMixed implements PyGalService {
-    private final Value pythonFunctionXY;
+    private final RenderXYFunction renderXYFunction;
 
     PyGalServiceMixed(GraalPyContext graalPyContext) {
-        pythonFunctionXY = graalPyContext.eval(
+        renderXYFunction = graalPyContext.eval(
                 // language=python
                 """
                         import pygal
@@ -30,12 +29,17 @@ def render_xy(title, label_datapoint_entries):
                                 xy_chart.add(entry.label(), entry.dataPoints())
                             return xy_chart.render().decode()
                         
-                        render_xy""");
+                        render_xy""").as(RenderXYFunction.class);
     }
 
     public record Entry(String label, double[][] dataPoints) {
     }
 
+    @FunctionalInterface
+    public interface RenderXYFunction {
+        String apply(String title, List<Entry> labelDatapointEntries);
+    }
+
     @Override
     public String renderXYChart() {
         String title = "XY Cosinus";
@@ -47,6 +51,6 @@ public String renderXYChart() {
                 new Entry("y = 1", new double[][]{{-5, 1}, {5, 1}}),
                 new Entry("y = -1", new double[][]{{-5, -1}, {5, -1}})
         );
-        return pythonFunctionXY.execute(title, labelDatapointEntries).asString();
+        return renderXYFunction.apply(title, labelDatapointEntries);
     }
 }
diff --git a/graalpy/graalpy-spring-boot-pygal-charts/src/main/resources/META-INF/native-image/com.example/demo/reachability-metadata.json b/graalpy/graalpy-spring-boot-pygal-charts/src/main/resources/META-INF/native-image/com.example/demo/reachability-metadata.json
index b8dcc03..56ad849 100644
--- a/graalpy/graalpy-spring-boot-pygal-charts/src/main/resources/META-INF/native-image/com.example/demo/reachability-metadata.json
+++ b/graalpy/graalpy-spring-boot-pygal-charts/src/main/resources/META-INF/native-image/com.example/demo/reachability-metadata.json
@@ -3,6 +3,9 @@
     {
       "type": "com.example.demo.PyGalServiceMixed$Entry"
     },
+    {
+      "type": "com.example.demo.PyGalServiceMixed$RenderXYFunction"
+    },
     {
       "type": "com.example.demo.PyGalServicePureJava$BytesIO"
     },
@@ -12,6 +15,13 @@
     {
       "type": "com.example.demo.PyGalServicePureJava$XY"
     },
+    {
+      "type": {
+        "proxy": [
+          "com.example.demo.PyGalServiceMixed$RenderXYFunction"
+        ]
+      }
+    },
     {
       "type": {
         "proxy": [