added listing to text

Author: habibasorour

source/ch7_recursion.ptx

@@ -129,7 +129,7 @@ public class MTools {
 
 
     <p>
-        First, let's see what happens if we try to write a recursive array sum function <em>without</em> using a helper method. In this approach, the user must provide the starting index, which is awkward and exposes implementation details:
+        First, let's see what happens if we try to write a recursive array sum function <em>without</em> using a helper method. In this approach, the user must provide the starting index, which is awkward and exposes implementation details. <xref ref="array-sum-python-no-helper" text="type-global"/> shows a Python version.
     </p>
     <listing xml:id="array-sum-python-no-helper">
     <program interactive="activecode" language="python">
@@ -160,7 +160,7 @@ main()
     </listing>
 
     <p>
-        This approach has a significant problem, namely that users must remember to start with index 0. Hence, the method signature is cluttered with an implementation detail, and it's easy to make a mistake by passing the wrong starting index. The same awkward pattern appears in Java:
+        <xref ref="array-sum-python-no-helper" text="type-global"/>'s approach has a significant problem, namely that users must remember to start with index 0. Hence, the method signature is cluttered with an implementation detail, and it's easy to make a mistake by passing the wrong starting index. The same awkward pattern appears in Java as shown in <xref ref="array-sum-java-no-helper" text="type-global"/>.
     </p>
     <listing xml:id="array-sum-java-no-helper">
     <program interactive="activecode" language="java">
@@ -191,7 +191,7 @@ public class ArrayProcessor {
         Both versions force users to understand and provide implementation details they shouldn't need to know about. Now let's see how helper methods solve this problem by providing a clean, user-friendly interface. Notice how the public method only requires the array itself, and the hidden recursive logic tracks the current index position.
     </p>
     <p>
-        Here's the improved Python version using a helper method:
+        <xref ref="array-sum-python-with-helper" text="type-global"/> shows the improved Python version using a helper method.
     </p>
     <listing xml:id="array-sum-python-with-helper">
     <program interactive="activecode" language="python">
@@ -234,7 +234,7 @@ main()
     </p>
 
     <p>
-        Now let's see the improved Java version using a helper method:
+        The same helper method pattern can be applied in Java, as shown in <xref ref="array-sum-java-with-helper" text="type-global"/>. The public method <c>sumArray</c> provides a clean interface, while the private helper method <c>sumHelper</c> manages the recursion and index tracking.
     </p>
     <listing xml:id="array-sum-java-with-helper">
     <program interactive="activecode" language="java">