hetu_script 0.0.5

Hetu is a lightweight script language written in Dart，intended to be embedded in Dart programs.

Hetu Script

Introduction

中文介绍

Hetu is a lightweight script language written purely in Dart. It is intended to be embedded in Flutter/Dart apps & games to enable hotfixes and scripting.

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

It meant to be used as a scripting language like lua, however, it is made to communicate with classes & functions in Dart very easily.

Syntax referrence

语法参考

In your Dart code, you can interpret an script file by this:

import 'package:hetu_script/hetu_script.dart';

void main() async {
  var hetu = HTInterpreter();
  hetu.evalf('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: String
  construct (name: String) {
    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()
}

Hetu's grammar is almost same to typescript, except a few things:

• Function is declared with 'fun'.
• Variable declared with keyword 'def' or 'let' and without a type will be given a type if it has an initialization.

Binding

To call Dart functions in Hetu, just init Hetu with 'externalFunctions'.

Then define those dart funtion in Hetu with 'external' keyword.

Then you can call those functions in Hetu.

You can pass object from Dart to Hetu by the return value of external functions.

You can pass object from Hetu to Dart by the return value of Interpreter's [invoke] function;

import 'package:hetu_script/hetu_script.dart';

void main() async {
  var hetu = HTInterpreter();
  await hetu.init(externalFunctions: {
    'hello': (List<dynamic> positionalArgs, Map<String, dynamic> namedArgs) => {'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');
}

And the output should be:

dart value: {greeting: hello}
hetu value: {greeting: hello, foo: bar}

Command line tool

On Windows, there is a hetu.exe under project directory to use in Command line.

Usage:

hetu [file_name] [invoke_func]

If no option is provided, enter REPL mode.

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

>>>var a = 42
42

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

>>>fun hello {\
return 6 * 7} // press enter
function hello(): any // repl print
>>>hello()
42 // repl print
>>>

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

If [invoke_name] is provided, evaluate the file in library mode and call a certain function with given name.