如何在JavaScript中表示代数数据类型和模式匹配

// Sum Type: 表示一个值可以是字符串或数字
const StringOrNumber = {
  isString: (value) => typeof value === 'string',
  isNumber: (value) => typeof value === 'number',
  createString: (value) => ({ type: 'string', value }),
  createNumber: (value) => ({ type: 'number', value })
};

// Product Type: 表示一个包含名字和年龄的对象
const Person = {
  create: (name, age) => ({ name, age })
};

// 模拟模式匹配函数
function match(value, patterns) {
  for (const [pattern, handler] of Object.entries(patterns)) {
    if (typeof pattern === 'function' && pattern(value)) {
      return handler(value);
    }
  }
  throw new Error('No matching pattern found');
}

// 使用示例
const result = match(
  { type: 'string', value: 'hello' },
  {
    [StringOrNumber.isString]: (value) => `It's a string: ${value.value}`,
    [StringOrNumber.isNumber]: (value) => `It's a number: ${value.value}`
  }
);

console.log(result); // 输出: It's a string: hello

function matchNested(value, patterns) {
  if (typeof value === 'object' && value !== null) {
    for (const [pattern, handler] of Object.entries(patterns)) {
      if (typeof pattern === 'function' && pattern(value)) {
        return handler(value);
      }
    }
  }
  throw new Error('No matching pattern found');
}

// 示例：处理嵌套对象
const nestedResult = matchNested(
  { type: 'person', value: { name: 'Alice', age: 30 } },
  {
    [Person.create]: (value) => `Name: ${value.name}, Age: ${value.age}`
  }
);

console.log(nestedResult); // 输出: Name: Alice, Age: 30