Constant evaluation support

editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/NullState.java

Index: editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/NullState.java
diff --git a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/NullState.java b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/NullState.java
new file mode 100644
index 0000000000000000000000000000000000000000..a4caca920fe5eb621e04fa811f5da53d1e2fe799
--- /dev/null
+++ b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/NullState.java
@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2013, the Dart project authors.
+ * 
+ * Licensed under the Eclipse Public License v1.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ * 
+ * http://www.eclipse.org/legal/epl-v10.html
+ * 
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.google.dart.engine.internal.object;
+
+import com.google.dart.engine.error.CompileTimeErrorCode;
+
+/**
+ * The unique instance of the class {@code NullState} represents the state of the value 'null'.
+ */
+public class NullState extends InstanceState {
+  /**
+   * An instance representing the boolean value 'true'.
+   */
+  public static final NullState NULL_STATE = new NullState();
+
+  /**
+   * Initialize a newly created state to represent the value 'null'.
+   */
+  private NullState() {
+    super();
+  }
+
+  @Override
+  public BoolState convertToBool() throws EvaluationException {
+    throw new EvaluationException(CompileTimeErrorCode.CONST_EVAL_THROWS_EXCEPTION);
+  }
+
+  @Override
+  public StringState convertToString() {
+    return new StringState("null");
+  }
+
+  @Override
+  public BoolState equalEqual(InstanceState rightOperand) throws EvaluationException {
+    assertBoolNumStringOrNull(rightOperand);
+    if (rightOperand instanceof DynamicState) {
+      return BoolState.UNKNOWN_VALUE;
+    }
+    return BoolState.from(rightOperand instanceof NullState);
+  }
+
+  @Override
+  public boolean equals(Object object) {
+    return object instanceof NullState;
+  }
+
+  @Override
+  public String getTypeName() {
+    return "Null"; //$NON-NLS-0$
+  }
+
+  @Override
+  public int hashCode() {
+    return 0;
+  }
+
+  @Override
+  public boolean isBoolNumStringOrNull() {
+    return true;
+  }
+
+  @Override
+  public BoolState logicalNot() throws EvaluationException {
+    throw new EvaluationException(CompileTimeErrorCode.CONST_EVAL_THROWS_EXCEPTION);
+  }
+
+  @Override
+  public String toString() {
+    return "null";
+  }
+}