手撸解释器教程-1

Hello Lox


// Your first Lox program!
print "Hello, world!";

数据类型

Booleans


true;  // Not false.
false; // Not *not* false.

Numbers


1234;  // An integer.
12.34; // A decimal number.

Strings


"I am a string";
"";    // The empty string.
"123"; // This is a string, not a number.

Nil

算数运算


add + me;
subtract - me;
multiply * me;
divide / me;

所有这些操作符都是针对数字的，将任何其他类型操作数传递给它们都是错误的。唯一的例外是+运算符——你也可以传给它两个字符串将它们串接起来。

比较与相等


less < than;
lessThan <= orEqual;
greater > than;
greaterThan >= orEqual;

1 == 2;         // false.
"cat" != "dog"; // true.

不同类型的值永远不会相等：


123 == "123"; // false.

反对隐式转换

逻辑运算


!true;  // false.
!false; // true.

true and false; // false.
true and true;  // true.

false or false; // false.
true or false;  // true.

优先级与分组


var average = (min + max) / 2;

语句


print "Hello, world!";

{
  print "One statement.";
  print "Two statements.";
}

变量


var imAVariable = "here is my value";
var iAmNil;

var breakfast = "bagels";
print breakfast; // "bagels".
breakfast = "beignets";
print breakfast; // "beignets".

控制流


if (condition) {
  print "yes";
} else {
  print "no";
}

var a = 1;
while (a < 10) {
  print a;
  a = a + 1;
}

for (var a = 1; a < 10; a = a + 1) {
  print a;
}

函数


makeBreakfast(bacon, eggs, toast);

makeBreakfast();

fun printSum(a, b) {
  print a + b;
}

fun returnSum(a, b) {
  return a + b;
}

执行到达代码块的末尾而没有return语句，则会隐式返回nil

闭包

在Lox中，函数是一等公民，这意味着它们都是真实的值，你可以对这些值进行引用、存储在变量中、传递等等。下面的代码是有效的：


fun addPair(a, b) {
  return a + b;
}

fun identity(a) {
  return a;
}

print identity(addPair)(1, 2); // Prints "3".

fun outerFunction() {
  fun localFunction() {
    print "I'm local!";
  }

  localFunction();
}

fun returnFunction() {
  var outside = "outside";

  fun inner() {
    print outside;
  }

  return inner;
}

var fn = returnFunction();
fn();

类


class Breakfast {
  cook() {
    print "Eggs a-fryin'!";
  }

  serve(who) {
    print "Enjoy your breakfast, " + who + ".";
  }
}

// Store it in variables.
var someVariable = Breakfast;

// Pass it to functions.
someFunction(Breakfast);

var breakfast = Breakfast();
print breakfast; // "Breakfast instance".

// 许您自由地向对象添加属性：
breakfast.meat = "sausage";
breakfast.bread = "sourdough";


class Breakfast {
  serve(who) {
    print "Enjoy your " + this.meat + " and " +
        this.bread + ", " + who + ".";
  }

  // ...
}

class Breakfast {
  init(meat, bread) {
    this.meat = meat;
    this.bread = bread;
  }

  // ...
}

var baconAndToast = Breakfast("bacon", "toast");
baconAndToast.serve("Dear Reader");
// "Enjoy your bacon and toast, Dear Reader."

继承


class Brunch < Breakfast {
  drink() {
    print "How about a Bloody Mary?";
  }
}

var benedict = Brunch("ham", "English muffin");
benedict.serve("Noble Reader");

class Brunch < Breakfast {
  init(meat, bread, drink) {
    super.init(meat, bread);
    this.drink = drink;
  }
}

标准库

无