1  // Copyright (c) 2024-2026 Tencent Zhuque Lab. All rights reserved.
 2  //
 3  // Licensed under the Apache License, Version 2.0 (the "License");
 4  // you may not use this file except in compliance with the License.
 5  // You may obtain a copy of the License at
 6  //
 7  //     http://www.apache.org/licenses/LICENSE-2.0
 8  //
 9  // Unless required by applicable law or agreed to in writing, software
10  // distributed under the License is distributed on an "AS IS" BASIS,
11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12  // See the License for the specific language governing permissions and
13  // limitations under the License.
14  //
15  // Requirement: Any integration or derivative work must explicitly attribute
16  // Tencent Zhuque Lab (https://github.com/Tencent/AI-Infra-Guard) in its
17  // documentation or user interface, as detailed in the NOTICE file.
18  
19  // Package parser 实现栈结构
20  package parser
21  
22  import (
23  	"container/list"
24  )
25  
26  // Stack represents a LIFO (Last In First Out) data structure
27  // 使用Go标准库中的list实现栈结构
28  type Stack struct {
29  	list *list.List
30  }
31  
32  // NewStack creates and initializes a new Stack
33  // 创建并初始化一个新的栈
34  func NewStack() *Stack {
35  	return &Stack{list: list.New()}
36  }
37  
38  // pop removes and returns the top element from the stack
39  // 从栈顶移除并返回元素，如果栈为空则返回nil
40  func (stack *Stack) pop() interface{} {
41  	e := stack.list.Back()
42  	if e != nil {
43  		stack.list.Remove(e)
44  		return e.Value
45  	}
46  	return nil
47  }
48  
49  // push adds a new element to the top of the stack
50  // 将新元素添加到栈顶
51  func (stack *Stack) push(v interface{}) {
52  	stack.list.PushBack(v)
53  }
54  
55  // isEmpty checks if the stack has no elements
56  // 检查栈是否为空
57  func (stack *Stack) isEmpty() bool {
58  	return stack.list.Len() == 0
59  }
60  
61  // top returns the top element without removing it from the stack
62  // 返回栈顶元素但不移除它，如果栈为空则返回nil
63  func (stack *Stack) top() interface{} {
64  	e := stack.list.Back()
65  	if e != nil {
66  		return e.Value
67  	}
68  	return nil
69  }