Changed signature of the optimize() method to return an RValue.

src/main/java/com/sk89q/worldedit/expression/runtime/Function.java

@@ -84,7 +84,7 @@ public class Function extends Node {
     }
 
     @Override
-    public Node optimize() throws EvaluationException {
+    public RValue optimize() throws EvaluationException {
         final RValue[] optimizedArgs = new RValue[args.length];
         boolean optimizable = !method.isAnnotationPresent(Dynamic.class);
         int position = getPosition();

src/main/java/com/sk89q/worldedit/expression/runtime/Node.java

@@ -34,7 +34,7 @@ public abstract class Node implements RValue {
     @Override
     public abstract String toString();
 
-    public Node optimize() throws EvaluationException {
+    public RValue optimize() throws EvaluationException {
         return this;
     }
 

src/main/java/com/sk89q/worldedit/expression/runtime/RValue.java

@@ -29,5 +29,5 @@ import com.sk89q.worldedit.expression.Identifiable;
 public interface RValue extends Identifiable {
     public double getValue() throws EvaluationException;
 
-    public Node optimize() throws EvaluationException;
+    public RValue optimize() throws EvaluationException;
 }

src/main/java/com/sk89q/worldedit/expression/runtime/Sequence.java

@@ -66,7 +66,7 @@ public class Sequence extends Node {
     }
 
     @Override
-    public Node optimize() throws EvaluationException {
+    public RValue optimize() throws EvaluationException {
         List<RValue> newSequence = new ArrayList<RValue>();
 
         RValue droppedLast = null;