修改默认程序

为了编写电话号码查询程序，创建一个新的main.mo文件‌

源码修改步骤‌

1. 编辑器中打开src/phonebook/main.mo 源码文件

2. 复制粘贴下面的示例代码到main.mo文件

// Import standard library functions for lists

import L "mo:base/List";
import A "mo:base/AssocList";

// The PhoneBook actor.
actor {

    // Type aliases make the rest of the code easier to read.
    public type Name = Text;
    public type Phone = Text;

    // The actor maps names to phone numbers.
    flexible var book: A.AssocList<Name, Phone> = L.nil<(Name, Phone)>();

    // An auxiliary function checks whether two names are equal.
    func nameEq(l: Name, r: Name): Bool {
        return l == r;
    };

    // A shared invokable function that inserts a new entry
    // into the phone book or replaces the previous one.
    public func insert(name: Name, phone: Phone): async () {
        let (newBook, _) = A.replace<Name, Phone>(book, name, nameEq, ?phone);
        book := newBook;
    };

    // A shared read-only query function that returns the (optional)
    // phone number corresponding to the person with the given name.
    public query func lookup(name: Name): async ?Phone {
        return A.find<Name, Phone>(book, name, nameEq);
    };
};

代码中有几个重点‌

• Name和Phone定义为自定义Text类型，像这样创建自定义类型可以增强代码可读性

• insert函数是一个update调用，lookup函数是一个query调用

• Phone类型通过?Phone定义为可选值