| /* |
| * Copyright (c) 1997, 2021 Oracle and/or its affiliates. All rights reserved. |
| * |
| * This program and the accompanying materials are made available under the |
| * terms of the Eclipse Distribution License v. 1.0, which is available at |
| * http://www.eclipse.org/org/documents/edl-v10.php. |
| * |
| * SPDX-License-Identifier: BSD-3-Clause |
| */ |
| |
| package com.sun.tools.xjc.reader.gbind; |
| |
| import java.util.Set; |
| |
| /** |
| * This builds content models. |
| * |
| * @author Kohsuke Kawaguchi |
| */ |
| public abstract class Expression { |
| |
| /** |
| * Computes {@code LAST(exp)} |
| */ |
| abstract ElementSet lastSet(); |
| |
| /** |
| * True of {@code \epsilon \in L(exp)} |
| */ |
| abstract boolean isNullable(); |
| |
| /** |
| * Builds up a DAG among {@link Element}s in this expression. |
| */ |
| abstract void buildDAG(ElementSet incoming); |
| |
| /** |
| * {@link Expression} that represents epsilon, the length-0 string. |
| */ |
| public static final Expression EPSILON = new Expression() { |
| ElementSet lastSet() { |
| return ElementSet.EMPTY_SET; |
| } |
| |
| boolean isNullable() { |
| return true; |
| } |
| |
| void buildDAG(ElementSet incoming) { |
| // noop |
| } |
| |
| public String toString() { |
| return "-"; |
| } |
| }; |
| } |