/// <summary>
/// 返回一个根为“ +”或“ - ”二进制运算符的 AST 树
/// </summary>
/// <returns></returns>
private static AstNode GetAdditiveAstTree()
{
AstNode left, right;
NodeType nodeType;
//获取更高优先级的左子树
left = GetMultiplicativeAstTree();
//token,正常情况应为运算符+或-运算符或终止符
//如果扫描结束
if (token == null)
return left;
while (true)
{
//+或-运算符
nodeType = ConvertToNodeType(token.TokenType);
//获取优先级更高的右子树，返回时可以明确是遇到了+或-运算符或终止符
right = GetMultiplicativeAstTree();
left = AstTree.MkAstNode(nodeType, left, right, 0);
//token,正常情况应为运算符+或-运算符或终止符
//如果扫描结束
if (token == null)
break;
}
return left;
}
/// <summary>
/// 返回AstTree
/// </summary>
/// <param name="ptp">优先级</param>
/// <returns></returns>
public static AstNode GetAstTree(int ptp = 0)
{
AstNode left, right;
NodeType nodeType;
token = ExecScan();
Console.WriteLine($"节点类型：{token?.TokenType.ToString()},节点值：{token?.IntValue}");
//第一个节点为左节点
left = GetAstLeafNode(token);
token = ExecScan();
Console.WriteLine($"节点类型：{token?.TokenType.ToString()},节点值：{token?.IntValue}");
//如果扫描结束
if (token == null)
{
return(left);
}
//运算符节点类型
nodeType = ConvertToNodeType(token.TokenType);
while (PrecedenceDic[nodeType] > ptp)
{
//优先级高的构建为右子树，遇到低优先级的运算符返回
right = GetAstTree(PrecedenceDic[nodeType]);
//合并子树
left = AstTree.MkAstNode(nodeType, left, right, 0);
//如果扫描结束
if (token == null)
{
break;
}
//更新当前令牌的详细信息,即低优先级令牌
nodeType = ConvertToNodeType(token.TokenType);
Console.WriteLine($"低优先级令牌:{PrecedenceDic[nodeType]}");
}
return(left);
}
/// <summary>
/// 返回一个根为“ * ”或“ / ”二进制运算符的 AST 树
/// </summary>
/// <returns></returns>
private static AstNode GetMultiplicativeAstTree()
{
AstNode left, right;
NodeType nodeType;
token = ExecScan();
Console.WriteLine($"节点类型：{token?.TokenType.ToString()},节点值：{token?.IntValue}");
//第一个节点为左节点
left = GetAstLeafNode(token);
//获取下一个token,正常情况应为运算符
token = ExecScan();
Console.WriteLine($"节点类型：{token?.TokenType.ToString()},节点值：{token?.IntValue}");
//如果扫描结束
if (token == null)
return left;
// 当token类型是*或/
while (token.TokenType == TokenType.STAR || token.TokenType == TokenType.SLASH)
{
nodeType = ConvertToNodeType(token.TokenType);
//获取下一个token
token = ExecScan();
Console.WriteLine($"节点类型：{token?.TokenType.ToString()},节点值：{token?.IntValue}");
right = GetAstLeafNode(token);
//合并左右节点
left = AstTree.MkAstNode(nodeType, left, right, 0);
//获取下一节点
token = ExecScan();
Console.WriteLine($"节点类型：{token?.TokenType.ToString()},节点值：{token?.IntValue}");
//如果扫描结束
if (token == null)
break;
}
return left;
}
