weekly 2024-07-29

Language Updates

• Simplified Error Handling Syntax: The syntax for capturing potential errors in function calls has been updated from f(x)!! to f?(x), which returns a Result type.

fn div(x: Int, y: Int) -> Int!String {
  if y == 0 {
    raise "division by zero"
  }
  x / y
}

fn main {
  let a = div?(10, 2)
  println(a) // Ok(5)
}

• JSON Literal Support: Added support for JSON literals. Numbers, strings, arrays, and dictionary literals are now overloaded to provide a JSON type, which can be used for constructing/matching JSON when the type is expected.

fn json_process(x: @json.JsonValue) -> Double {
  match x {
    {
      "outer": {
        "middle": {
          "inner": [
            { "x": Number(x) },
            { "y": Number(y) }
          ]
        }
      }
    } => x + y
    _ => 0
  }
}

fn main {
  let x: @json.JsonValue = {
    "outer": { "middle": { "inner": [{ "x": 42 }, { "y": 24 }] } },
    "another_field": "string value",
  }
  json_process(x) |> println
}

• Derive Hash Support: Added derive(Hash) to automatically generate implementations of the Hash trait for types.

enum MyType {
  C1
  C2(Int)
} derive(Eq, Hash)

fn main {
  let m = {}..set(C1, 1)..set(C2(1), 2)..set(C2(2), 3)
  println(m[C1]) // Some(1)
  println(m[C2(1)]) // Some(2)
  println(m[C2(3)]) // None
}

• JavaScript Backend Update: Removed dependency on TextDecoder in generated code.

Core Updates

• Function Signature Changes:

  • Array::new_with_index -> Array::makei
  • FixedArray::new / FixedArray::new_with_index -> FixedArray::makei
  • FixedArray::empty -> FixedArray::new

• Removed Debug Trait

Build System Updates

• Single .mbt File Support: Now supports running a single .mbt file (not within a package). Usage: moon run xx.mbt (links to the standard library by default, requires a main function in xx.mbt).

• Shell Completion: Moon now supports shell completion.

  Example Usage: Zsh

  Zsh automatically reads all scripts under $FPATH on startup. You can place the completion script in any path under $FPATH.

  To manage more conveniently, create a new path for completions $ZSH/completions and add it to $FPATH.

  mkdir $ZSH/completions
  echo "FPATH+=$ZSH/completions" >> ~/.zshrc
  moon shell-completion > $ZSH/completions/_moon
  . ~/.zshrc # Reload to use, or omz reload

  To maintain portability, you can directly add the following line to .zshrc:

  eval "$(moon shell-completion --shell=zsh)"

  

  For the effect shown in the pic, you also need to install the zsh-autocomplete and zsh-autosuggestions plugins.

Toolchain Updates

• moonfmt Fixes:

  Fixed an issue with array spread formatting adding braces.

  Adjusted parenthesis inference for pattern matching to avoid using wildcards.

• VS Code Auto-test Support: Now supports automatic test generation for functions, including black-box tests (ending in _test.mbt) and white-box tests (unit tests).

• Run | Debug Buttons for .mbt: Added support for single .mbt file Run | Debug buttons.