E4134

The return type of this anonymous function is expected to include an error type. Please add the error type to the return type annotation or use fn! instead.

错误示例

fn main {
  let draw : (Int) -> Int! = fn(luck : Int) -> Int {
    //                                         ^~~
    // Error: The return type of this anonymous function is expected include an
    // error type. Please add the error type to the return type annotation or
    // use `fn!` instead.
    if luck == 7 {
      return 42
    }
    fail!("Bad luck") // E4122 as well
  }
  try {
    println("Draw: \{draw!(7)}")
  } catch {
    error => println("Error: \{error}")
  }
}

建议

Add the error type to the return type annotation:

fn main {
  let draw : (Int) -> Int! = fn(luck : Int) -> Int! {
    if luck == 7 {
      return 42
    }
    fail!("Bad luck")
  }
  try {
    println("Draw: \{draw!(7)}")
  } catch {
    error => println("Error: \{error}")
  }
}