weekly 2024-06-17

Language Update

• Supported error handling:

1. Functions can now specify return types with error handling using the syntax Int!String. The following example means the function returns an Int under normal conditions, and throws an error of type String otherwise.

fn div(x: Int, y: Int) -> Int!String { .. }

2. The raise keyword is used to interrupt the current control flow and throw an error. For example:

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

3. The expression try { expr0 } catch { pattern1 => expr1; pattern2 => expr2; .. } can be used to catch errors thrown in expr0 and handle them with pattern matching. For example, the following function calls the div function and prints the error message if an error is thrown, then returns a default value:

fn div_with_default(x: Int, y: Int, default: Int) -> Int {
  try {
    div(x, y)!
  } catch {
    s => { println(s); default }
  }
}

4. Additionally, the suffix operators ! and !! are available for error handling. These operators can only be used on function calls: f(x)! rethrows any error immediately. f(x)!! panics on any error, equivalent to:

try { f(x)! } catch { _ => panic() }

Function calls include method calls, infix operators, and pipeline operators, such as:

fn init {
  let _ = x.f()!!
  let _ = (x + y)!!
  let _ = (x |> f)!!
}

5. Last, functions that might throw errors but do not use any of the above error handling mechanisms will result in an "unhandled error" error.

• Support Map literal syntax.

fn init {
  // Keys must be literals
  let m1 : Map[String, Int] = { "x": 1, "y": 2 }
  let m2 : Map[Int, String] = { 1: "x", 2: "y" }
}

IDE Update

• Fixed a bug where methods from the builtin package would appear twice during autocompletion.

• Fixed a bug where the Byte type was missing from autocompletion options.

Build System Update

• Added support for internal packages. These packages are placed in a directory named internal and can only be imported by packages rooted in the parent directory of internal.

  For example, if a package is located at username/hello/x/internal/a, its parent directory is username/hello/x. Only username/hello/x and its subpackages (e.g., username/hello/x/a) can import username/hello/x/internal/a. However, username/hello/y cannot import this package.