Hetu Script

Warning

Hetu is early WIP! We are focusing on making Hetu stable and feature complete right now.

Discussion group:

Discord: https://discord.gg/Q8JWQYEw

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Introduction

Hetu is a lightweight script language purely written in Dart for embedding in Flutter apps. The main goal is to enable Flutter app have hotfix and scripting ability.

We did not choose to use another existing language to achieve the goal. Because we want to keep the language simple, and keep it away from interference of other language's complex implementation and their irrelative-to-Flutter eco-system, and make the debug process pain-free and remain in Dart realms.

It takes very little time to bind almost anything in Dart/Flutter into Hetu and use similar grammar to write your app. And to communicate with classes & functions in Dart is very easy.

Quick start

Hetu's grammar is close to typescript/kotlin/swift and other modern languages, need very little time to get familar with.

  • Optional semicolon.
  • Function is declared with 'fun, get, set, construct'.
  • Optional type annotation. Variable declared with 'let, const' will infer its type from its initializer expression.

Syntax referrence

In your Dart code, you can interpret a script file:

import 'package:hetu_script/hetu_script.dart';

void main() async {
  var hetu = Hetu();
  await hetu.init();
  await hetu.import('hello.ht', invokeFunc: 'main');
}

While hello.ht is the script file written in Hetu, here is an example:

// Define a class.
class Person {
  var name: str
  construct (name: str) {
    this.name = name
  }
  fun greeting {
    print('Hi! I\'m', name)
  }
}

// This is where the script starts executing.
fun main {
  var ht = Person('Hetu')
  ht.greeting()
}

Binding

Hetu script is purely written in Dart, so passing object to and from script is extremely easy.

Check this page for more information about how to bind external classes, functions, enums and how to passing object and functions between Dart and script.

import 'package:hetu_script/hetu_script.dart';

void main() async {
  var hetu = Hetu();
  await hetu.init(externalFunctions: {
    'hello': () => {'greeting': 'hello'},
  });
  await hetu.eval(r'''
      external fun hello
      fun main {
        var dartValue = hello()
        print('dart value:', dartValue)
        dartValue['foo'] = 'bar'
        return dartValue
      }''');

  var hetuValue = hetu.invoke('main');

  print('hetu value: $hetuValue');
}

Command line tool

Hetu has a command line REPL tool for testing. You can activate by the following command:

dart pub global activate hetu_script

Then you can use the following command in any directory on your computer. (If you are facing any problems, please check this official document about pub global activate)


hetu [file_name] [invoke_func]

If file_name is provided, evaluate the file in function mode.

If invoke_func is provided, evaluate the file in module mode and call a certain function with given name.

If no option is provided, enter REPL mode.

In REPL mode, every exrepssion you entered will be evaluated and print out immediately.

If you want to write multiple line in REPL mode, use '\' to end a line.

>>>var a = 42
>>>a
42
>>>fun hello {\
return a }
>>>hello
function hello() -> any // repl print
>>>hello()
42 // repl print
>>>

Referrences:

Apps that embedded Hetu:

NameAuthorDescriptionDownloadSource
Monster Hunter CompanionrockingdiceAndroid
iOS

Libraries

hetu_script
HETU SCRIPT 0.0.1 [...]