河图中提供的 API
河图中的一些基础类型本身是 Dart 类型，同时也默认绑定了大多数 Dart 中的 api。例如下面这些类型和其对象都可以在脚本中直接使用：number, int, double, bool, String, List, Set, Map。
例如，我们可以在脚本中使用 dart 中的列表上提供的 map 接口：
final result = range(10).map((value) => 'row: ${value}')
全局函数
下面是一些脚本中可以直接使用的函数：
external function print(... args: any)
external function stringify(obj: any)
external function jsonify(obj)
external function range(startOrStop: number, [stop: number, step: number]) -> Iterable
eval()
此外，和 Javascript 一样，脚本中包含一个用以解释自己的接口 eval()：
import 'package:hetu_script/hetu_script.dart';
void main() {
final hetu = Hetu();
hetu.init();
final result = hetu.eval(r'''
final meaning = eval("6 * 7")
meaning
''');
print(result);
}
对象字面量
河图中包含类似 Javascript 的对象字面量语法。并且也实现了基本的原型链。
河图中所有的对象字面量都有一个原型对象，并且在这个原型对象上预先定义了一些常用接口：
struct Object {
/// Create a struct from a dart Json data
/// Usage:
/// ```
/// var obj = Object.fromJson(jsonDataFromDart)
/// ```
external static function fromJson(data) -> {}
/// Get the List of the keys of this struct
external get keys -> List
/// Get the List of the values of this struct
/// The values are copied,
/// you cannot modify the struct in this way
external get values -> List
/// Check if this struct has a key in its own fields.
external function containsKey(key: string) -> bool
/// Check if this struct has a key
/// in its own fields or its prototypes' fields.
external function contains(key: string) -> bool
/// Check if this struct is empty.
external get isEmpty -> bool
/// Check if this struct is not empty.
external get isNotEmpty -> bool
/// Get the number of the members of this struct.
/// Will not include the members of its prototypes.
external get length -> int
/// Create a new struct form deepcopying this struct
external function clone() -> {}
/// Create dart Json data from this struct
function toJSON() -> Map => jsonify(this)
function toString() -> string => stringify(this)
}
大多数上面这些方法都可以直接在对象上调用。例如：
final obj = { a: 42 }
obj.contains('a') // true
对于 static 方法，需要通过原型的名字来调用：
final book = Object.fromJson(data);
Math
脚本中提供了 Dart 中 Random 对象的绑定，用来生成随机数，并且提供了一些额外的辅助 api，例如获取随机颜色，以及获取一个列表中的随机对象等。
脚本中将 Dart 的 Math 库，绑定为了一个静态类，内置了一些数学相关的常数和接口。
external class Random {
constructor ([seed: int])
function nextBool -> bool
function nextInt(max: int) -> int
function nextDouble() -> float
function nextColorHex({hasAlpha: bool = false}) -> string
function nextBrightColorHex({hasAlpha: bool = false}) -> string
function nextIterable(list: Iterable) -> any
function shuffle(list: Iterable) -> Iterable
}
external class Math {
static const e: float = 2.718281828459045
static const pi: float = 3.1415926535897932
/// Convert [radians] to degrees.
static function degrees(radians)
/// Convert [degrees] to radians.
static function radians(degrees)
static function radiusToSigma(radius: float) -> float
/// Box–Muller transform for generating normally distributed random numbers between [min : max].
static function gaussianNoise(mean: float, standardDeviation: float, {min: float, max: float, randomGenerator}) -> float
/// Noise generation function provided by [fast_noise](https://pub.dev/packages/fast_noise) package.
/// Noise types: perlin, perlinFractal, cubic, cubicFractal
static function noise2d(width, height, {seed, noiseType = 'cubic', frequency = 0.01})
/// Return the smaller value between a & b.
/// If one of them is null, return the other value.
static function min(a, b)
/// Return the greater value between a & b.
/// If one of them is null, return the other value.
static function max(a, b)
static function sqrt(x: number) -> number
static function pow(x: number, exponent: number) -> number
static function sin(x: number) -> number
static function cos(x: number) -> number
static function tan(x: number) -> number
static function exp(x: number) -> number
static function log(x: number) -> number
static function parseInt(source: string, {radix: int?}) -> number
static function parseDouble(source: string) -> number
static function sum(list: List<number>) -> number
static function checkBit(index: int, check: int) -> bool
static function bitLS(x: int, distance: int) -> bool
static function bitRS(x: int, distance: int) -> bool
static function bitAnd(x: int, y: int) -> bool
static function bitOr(x: int, y: int) -> bool
static function bitNot(x: int) -> bool
static function bitXor(x: int, y: int) -> bool
}
Hash
脚本中定义了一个静态类 Hash ，内置了一些字符串加密相关的接口。
external class Hash {
static function uid4([repeat: int?]) -> string
static function crcString(data: string, [crc: string = 0]) -> string
static function crcInt(data: string, [crc: string = 0]) -> int
}