Vol.59 MoonBit Update 1104

[Kuki]

2024-11-04

Language Updates

• Compile-time Constants Support
  • Introduced support for constants declared with const C = ..., where names start with uppercase letters. Must be built-in numeric types or String. Constants can be used as regular values and for pattern matching. Currently, the values of constants can only be literals.

const MIN_INT = 0x1000_0000
const MAX_INT = 0x7fff_ffff

fn classify_int(x : Int) -> Unit {
  match x {
    MIN_INT => println("smallest int")
    MAX_INT => println("largest int")
    _ => println("other int")
  }
}

fn main {
  classify_int(MIN_INT) // smallest int
  classify_int(MAX_INT) // largest int
  classify_int(42) // other int
}

• Improved Unused Warnings

1. Added detection for unused parameters in enum:

enum E {
  // Compiler warns if y is unused
  C(~x : Int, ~y : Int) 
}

fn f(x : E) -> Unit {
  match x {
    C(~x, ..) => println(x)
  }
}

fn main {
  f(C(x=1, y=2))
}

2. Added detection for unused default parameter values (default off):

// The function `f` is private and that the caller always provides a value for `x` explicitly when calling it.
// If warning 32 is enabled (which is off by default), the compiler will notify the developer that the default value for `x` is unused.
fn f(~x : Int = 0) -> Unit {
  println(x)
}

fn main {
  f(x=1)
}

• Direct Function Imports
  • Functions from other packages can now be directly imported without the @pkg. prefix. To set this up, you must declare the functions in the "value" field of the moon.pkg.json configuration file.

{
  "import": [
    { 
      "path": "moonbitlang/pkg",
      "alias": "pkg",
      "value": ["foo", "bar"]
    }
  ]
}

In this example, the functions foo and bar from the package moonbitlang/pkg can be called directly without the prefix @pkg..

• Native JavaScript BigInt Support

  • BigInt type compiles to native JavaScript BigInt, with efficient pattern matching using switch statements.

• Experimental: JavaScript backend generates .d.ts for exported functions

  • JavaScript backend now generates .d.ts files based on exported functions specified in moon.pkg.json, enhancing TypeScript/JavaScript integration. (*This feature for exporting complex types is still under design, and for now, it generates TypeScript’s any type.)

IDE Updates

• Block-line Support

  • Introduced special block-line markers (///|) in top-level comments (///) to enhance code readability and structure:
    

    

  • Use moon fmt --block-style can automatically add these markers. In the future, incremental code parsing and type checking based on block-line markers will further enhance the responsiveness and usability of the Language Server Protocol (LSP), improving development efficiency.

• Test Coverage Visualization

  • Added support for visualizing test coverage in the test explorer:
    
    

• AI Features

  • Added /doc-pub command for generating documentation for public functions.
  • Fixed issue where /doc command would overwrite pragmas.
  • Patch now verifies generated test cases:
    
    

Build System Updates

• Package Checking
  • moon check supports checking specified packages and their dependencies: moon check /path/to/pkg.

MoonBit Markdown Library

• Open Source
  • The MoonBit Markdown library is now open source, and available for download on MoonBit’s package manager mooncakes.io.