E4119

This function is not a toplevel function, so it cannot have labelled arguments.

Erroneous example

fn main {
  fn greet(name~ : String) -> Unit {
    println("Hello, \{name}")
  }
}

Suggestion

You can either remove the labelled argument, using positional argument instead:

fn main {
  fn greet(name : String) -> Unit {
    println("Hello, \{name}")
  }
  greet("world")
}

Or you can make the function a toplevel function:

fn greet(name~ : String) -> Unit {
  println("Hello, \{name}")
}

fn main {
  greet(name="World")
}