weekly 2024-03-18
MoonBit is a Rust-like language (with GC support) and toolchain optimized for WebAssembly experience. This is our recent update:
Language Update
1. Experimental support for default method in trait
trait MyShow {
repr(Self) -> String
str (Self) -> String // it has a default implementation
}
impl MyShow::str(self : Self) -> String {
// default implementation of str
self.repr()
}
type MyInt Int
fn repr(self:MyInt) -> String {
self.0.to_string()
}
// Now MyInt implements MyShow now
2. The type parameters of type definitions can be _, which can be used to define phantom types to restrict some logically illegal operations in the program. For example, we want to prevent adding lengths of different units together:
type Length[_] Int
type Kilometer
type Mile
fn add[T](x: Length[T], y:Length[T]) -> Length[T] {
Length::Length(x.0 + y.0)
}
let d_km: Length[Kilometer] = Length(10)
let d_mile: Length[Mile] = Length(16)
At this point, lengths with different units cannot be directly added:
fn init {
add(d_km, d_mile) |> ignore
// ^~~~~~ Error: Expr Type Mismatch
}
However, lengths with the same units can be added:
fn init {
add(d_km,d_km) |> ignore
// OK
}
3. Now, a top-level function without a marked return value is an error.
fn print_hello() {
// ^~~~~~~~~~~ Error:
// Missing type annotation for the return value.
println("Hello!")
}
4. Added the bitwise NOT operator.
fn main {
println((1).lnot())
}
Output:
-2
5. Improved the output of List::to_string/debug_write.
fn main {
let l = List::Cons(1, Cons(2, Cons(3, Nil)))
println(l)
}
Output:
List::[1, 2, 3]
6. Added the Byte type.
The byte literals are prefixed by b. The following snippet demonstrates its usage:
fn init {
let b1 = b'a'
println(b1.to_int())
let b2 = b'\xff'
println(b2.to_int())
}
More utility methods on Byte type are around the corner.
IDE Update
1. Added support for autocompletion of moonbitlang/core.
2. Formatting Update：
a. Adjust empty structs, enums, and traits to avoid blank lines.
Before：
struct A {
}
After：
struct A {}
b. Fixed incorrect indentation for continue
c. Fixed issues with semicolons appearing after formatting multiline statements