Compiler errors 智能合约代码中预期的未识别错误-混音

编译器报告下面附加的错误；很奇怪，我正在跟随课程的导师，导师建议我使用旧版本的混音，我在类似的问题中读到“returns”应该是单数，但他的代码编译没有问题，我还是尝试了，没有成功；他正在使用^0.4.11我正在运行^0.8.4，尽管当我降级到以前的版本时问题仍然存在

错误：

ParseError: Expected '{' but
got 'constant' -->
tests/pendulum_ico.sol:28:60: |
28 | function 
equity_in_pendulum(address 
investor) external constant 
returns (uint) { | ^^^^^^^^

pragma solidity ^0.8.3;

contract pendulum_ico {
    
// Introducing the maximum number of Pendulum available for sale

    uint public max_pendulum = 1000000;
    
// Introducing the USD to Pendulum conversion relocatable

    uint public usd_to_pendulum = 1000;
    
// Introducing the total number of Pendulum that have been bought by the investors

    uint public total_pendulum_bought = 0;
    
// Mapping from the investor address to its equity in Pendulum and usd_to_pendulum

    mapping(address => uint) equity_pendulum;
    mapping(address => uint) equity_usd;
    
// Checking if an investor can buy Pendulum

    modifier can_buy_pendulum(uint usd_invested) {
        require (usd_invested * usd_to_pendulum + total_pendulum_bought <= max_pendulum);
        _;
    }
    
// Getting the equity in Pendulum of an investor

    function equity_in_pendulum(address investor) external constant returns (uint) { 
        return equity_pendulum[investor];
    }                             
    
// Getting the equity in USD of an investor

    function equity_in_usd(address investor) external constant returns (uint) {
        return equity_usd[investor];
    }
    
// Buying Pendulum 

    function buy_pendulum(address investor, uint usd_invested) external
    can_buy_pendulum(usd_invested) {
        uint pendulum_bought = usd_invested * usd_to_pendulum;
        equity_pendulum[investor] += pendulum_bought;
        equity_usd[investor] = equity_pendulum[investor] / 1000;
        total_pendulum_bought += hadcoins_bought;
        
    }
    
// Selling Pendulum 

    function sell_pendulum(address investor, uint pendulum_sold) external {
        equity_pendulum[investor] -= pendulum_sold;
        equity_usd[investor] = equity_pendulum[investor] / 1000;
        total_pendulum_bought -= pendulum_sold;
    }
    
}

代码：

ParseError: Expected '{' but
got 'constant' -->
tests/pendulum_ico.sol:28:60: |
28 | function 
equity_in_pendulum(address 
investor) external constant 
returns (uint) { | ^^^^^^^^

pragma solidity ^0.8.3;

contract pendulum_ico {
    
// Introducing the maximum number of Pendulum available for sale

    uint public max_pendulum = 1000000;
    
// Introducing the USD to Pendulum conversion relocatable

    uint public usd_to_pendulum = 1000;
    
// Introducing the total number of Pendulum that have been bought by the investors

    uint public total_pendulum_bought = 0;
    
// Mapping from the investor address to its equity in Pendulum and usd_to_pendulum

    mapping(address => uint) equity_pendulum;
    mapping(address => uint) equity_usd;
    
// Checking if an investor can buy Pendulum

    modifier can_buy_pendulum(uint usd_invested) {
        require (usd_invested * usd_to_pendulum + total_pendulum_bought <= max_pendulum);
        _;
    }
    
// Getting the equity in Pendulum of an investor

    function equity_in_pendulum(address investor) external constant returns (uint) { 
        return equity_pendulum[investor];
    }                             
    
// Getting the equity in USD of an investor

    function equity_in_usd(address investor) external constant returns (uint) {
        return equity_usd[investor];
    }
    
// Buying Pendulum 

    function buy_pendulum(address investor, uint usd_invested) external
    can_buy_pendulum(usd_invested) {
        uint pendulum_bought = usd_invested * usd_to_pendulum;
        equity_pendulum[investor] += pendulum_bought;
        equity_usd[investor] = equity_pendulum[investor] / 1000;
        total_pendulum_bought += hadcoins_bought;
        
    }
    
// Selling Pendulum 

    function sell_pendulum(address investor, uint pendulum_sold) external {
        equity_pendulum[investor] -= pendulum_sold;
        equity_usd[investor] = equity_pendulum[investor] / 1000;
        total_pendulum_bought -= pendulum_sold;
    }
    
}

pragma-solidity^0.8.3；
合同钟摆{
//介绍可供销售的摆锤的最大数量
uint公共最大摆锤=1000000；
//引入美元到钟摆转换可重新定位
uint公共美元对美元=1000；
//介绍投资者购买的钟摆总数量
uint公共总购买量=0；
//从投资者地址到其在钟摆和美元对钟摆中的权益的映射
映射（地址=>uint）权益；
映射（地址=>uint）权益单位美元；
//检查投资者是否可以购买钟摆
修改器可购买摆锤（单位投资美元）{
要求（从0.4 a到0.5 a之间购买的美元投资*美元对钟摆+总钟摆：

现在不允许使用
常量
作为函数状态可变修饰符


在0.8中，还可以将函数声明为，它符合0.4
常量中定义的状态不变性标准

function equity_in_pendulum(address investor) external view returns (uint) { 
    return equity_pendulum[investor];
}

彼得，你不知道自己帮了多少忙。