The MoonBit Update——1204

In December 2023, MoonBit underwent Alpha testing. This post aims to introduce recent updates to MoonBit’s language and toolchain, along with applications developed using MoonBit.

Changes in MoonBit Language

1. MoonBit Debugger is now available for use.

Use the build command moon build --debug --target wasm-gc to support outputting sourcemap, which can be used for source debugging in browser. For specific usage, please refer to the example at GitHub - moonbit/moonbit-debugging-example.

2. Optimized layout for enum data types with only constant constructors.

For instance, in the following code, the optimization will now represent A and B directly as integers 0 and 1, eliminating the need for boxing and unboxing operations.

enum T {

fn init {
  let t = T::A
  match t {
    A => println(0)
    B => println(1)

3. Reference types are non-nullable at function boundaries.

This paves the way for a stable ABI for the builtin data types, such as String, Array, etc.

Build System

Removed the name field in moon.pkg.json. The entry point is no longer identified by "name": "main", but explicitly using "is_main": true instead.


We’ve launched a new process for modifying MoonBit language features, the GitHub link is here: GitHub - moonbitlang/moonbit-RFCs: RFCs of MoonBit lang.

This will be the hub for all our language feature ideas.Plus, we welcome anyone passionate about language features to contribute.