2024-12-30

Language Update

• Added labeled loop syntax, which allows you to jump directly to a specified layer in a multi-layer loop, using ~ as the suffix for the label.

fn f[A](xs : ArrayView[A], ys : Iter[Int]) -> @immut/list.T[(Int, A)] {
  l1~: loop 0, xs, @immut/list.Nil {
    _, [], acc => acc
    i, [x, .. as rest], acc =>
      for j in ys {
        if j == i {
          continue l1~ i + 1, rest, @immut/list.Cons((j, x), acc)
        }
        if j + i == 7 {
          break l1~ acc
        }
      } else {
        continue i - 1, rest, acc
      }
  }
}

• New Discard Argument, function arguments named with a single underscore will be discarded, multiple arguments can be discarded within the same function.

fn positional(a : Int, b : Int) -> Int {
  a + b
}

fn discard_positional(_: Int, _: Int) -> Int {
  1
}

• The semantics of pub have officially changed from being fully public to read-only, and the pub(readonly) syntax has been deprecated. To declare a fully public type/struct/enum, you should now use pub(all). To declare a fully public (externally implementable) trait, use pub(open). This change was previously announced via a warning, and if you already followed the warning and updated pub to pub(all) or pub(open), you only need to replace pub(readonly) with pub to complete the migration. The moon fmt tool can automatically convert pub(readonly) to pub.

• In the future, the behavior where a trait will fallback to method implementation if no explicit implementation is found may be removed. We encourage new code to use the explicit impl Trait for Type syntax instead of relying on methods for trait implementation. In cases of no ambiguity, you can still use dot syntax (impl Trait for Type with method(...)), so adopting explicit impl syntax won't sacrifice convenience.

• The old prefix syntax for labeled parameters has been removed.

• The old syntax for accessing newtype contents using .0 has been removed. Additionally, if a newtype contains a tuple, index access like .0, .1, etc., will now automatically forward to the tuple inside the newtype. For example:

type Tuple (Int, String)

fn main {
  let t = (4, "2")
  println(t.0) // 4
  println(t.1) // 2
}

• Parameters have been added to derive(FromJson) and derive(ToJson) to control the specific behavior and data layout of type serialization and deserialization. The detailed changes can be found in Docs > Language > Deriving.

  You can now rename fields and adjust the serialization format of enums. The specific behavior of JSON serialization and deserialization may be optimized and changed in the future.

enum UntaggedEnum {
  C1(Int)
  C2(String)
} derive(ToJson(repr(untagged)), Show)
// { "0": 123 }, { "0": "str" }

enum InternallyTaggedEnum {
  C1(Int)
  C2(String)
} derive(ToJson(repr(tag="t")), Show)
// { "t": "C1", "0": 123 }

enum ExternallyTaggedEnum {
  C1(Int)
  C2(String)
} derive(ToJson(repr(ext_tagged)), Show)
// { "C1": { "0": 123 } }

enum AdjacentlyTaggedEnum {
  C1(Int)
  C2(String)
} derive(ToJson(repr(tag="t", contents="c")), Show)
// { "t": "C1", "c": { "0": 123 } }

struct FieldRenameAllCamel {
  my_field : Int
} derive(ToJson(rename_all="camelCase", repr(tag="t")), Show)
// { "t": "fieldRenameAllCamel", "myField": 42 }

struct FieldRenameAllScreamingSnake {
  my_field : Int
} derive(ToJson(rename_all="SCREAMING_SNAKE_CASE", repr(tag="t")), Show)
// { "t": "FIELD_RENAME_ALL_SCREAMING_SNAKE", "MY_FIELD": 42 }

IDE Update

• IDE now supports gotodef/gotoref/rename for loop label.

• Document symbols are now displayed in a hierarchical way in the IDE, as follows.

• Fixed bug in white box testing regarding type renaming.

• Added IDE support for automatically omitting parameter inlay hints in case of repetition.

• IDE adds value tracing. Clicking on "Trace" codelen above the main function will enable it, and clicking again will disable it.

  • For variables inside a loop, only the latest value and the hit count are shown.

Build System Update

• moon adds a --no-strip parameter to preserve symbol information in release build mode.

Document Update

• Fixed an issue where MoonBit Tour's theme was not maintained when switching pages.

• Added range, range pattern and newtype sections to MoonBit Tour.