Improved the expression parser's optimizer.

Added optimizers for Conditional, For, SimpleFor and While.
Improved the Sequence optimizer.
Removed the optimizer TODOs from Break and Return.

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

@@ -47,6 +47,4 @@ public class Break extends Node {
     public String toString() {
         return doContinue ? "continue" : "break";
     }
-
-    //TODO: optimizer
 }

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

@@ -42,7 +42,7 @@ public class Conditional extends Node {
         if (condition.getValue() > 0.0) {
             return truePart.getValue();
         } else {
-            return falsePart == null ? 0 : falsePart.getValue();
+            return falsePart == null ? 0.0 : falsePart.getValue();
         }
     }
 
@@ -62,5 +62,18 @@ public class Conditional extends Node {
         }
     }
 
-    //TODO: optimizer
+    @Override
+    public RValue optimize() throws EvaluationException {
+        final RValue newCondition = condition.optimize();
+
+        if (newCondition instanceof Constant) {
+            if (newCondition.getValue() > 0) {
+                return truePart.optimize();
+            } else {
+                return falsePart == null ? new Constant(getPosition(), 0.0) : falsePart.optimize();
+            }
+        }
+
+        return new Conditional(getPosition(), newCondition, truePart.optimize(), falsePart.optimize());
+    }
 }

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

@@ -74,5 +74,17 @@ public class For extends Node {
         return "for (" + init + "; " + condition + "; " + increment + ") { " + body + " }";
     }
 
-    //TODO: optimizer
+    @Override
+    public RValue optimize() throws EvaluationException {
+        final RValue newCondition = condition.optimize();
+
+        if (newCondition instanceof Constant && newCondition.getValue() <= 0) {
+            // If the condition is always false, the loop can be flattened.
+            // So we run the init part and then return 0.0.
+            return new Sequence(getPosition(), init, new Constant(getPosition(), 0.0)).optimize();
+        }
+
+        //return new Sequence(getPosition(), init.optimize(), new While(getPosition(), condition, new Sequence(getPosition(), body, increment), false)).optimize();
+        return new For(getPosition(), init.optimize(), newCondition, increment.optimize(), body.optimize());
+    }
 }

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

@@ -47,6 +47,4 @@ public class Return extends Node {
     public String toString() {
         return "return " + value;
     }
-
-    //TODO: optimizer
 }

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

@@ -88,6 +88,10 @@ public class Sequence extends Node {
             newSequence.add(droppedLast);
         }
 
+        if (newSequence.size() == 1) {
+            return newSequence.get(0);
+        }
+
         return new Sequence(getPosition(), newSequence.toArray(new RValue[newSequence.size()]));
     }
 }

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

@@ -78,5 +78,10 @@ public class SimpleFor extends Node {
         return "for (" + counter + " = " + first + ", " + last + ") { " + body + " }";
     }
 
-    //TODO: optimizer
+    @Override
+    public RValue optimize() throws EvaluationException {
+        // TODO: unroll small loops into Sequences
+
+        return new SimpleFor(getPosition(), (LValue) counter.optimize(), first.optimize(), last.optimize(), body.optimize());
+    }
 }

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

@@ -95,5 +95,21 @@ public class While extends Node {
         }
     }
 
-    //TODO: optimizer
+    @Override
+    public RValue optimize() throws EvaluationException {
+        final RValue newCondition = condition.optimize();
+
+        if (newCondition instanceof Constant && newCondition.getValue() <= 0) {
+            // If the condition is always false, the loop can be flattened.
+            if (footChecked) {
+                // Foot-checked loops run at least once.
+                return body.optimize();
+            } else {
+                // Loops that never run always return 0.0.
+                return new Constant(getPosition(), 0.0);
+            }
+        }
+
+        return new While(getPosition(), newCondition, body.optimize(), footChecked);
+    }
 }