E1018

There is no continue in this loop expression, so loop is useless here.

This error occurs when using a loop expression that contains no continue statement. In MoonBit, a loop without any continue statements is equivalent to an block expression that will be executed only once, making the loop keyword redundant in such cases. You should either add a continue statement if you need to restart the loop from the beginning, or use a simpler control flow construct like match or if.

Erroneous example

fn countdown(n : Int) -> Int {
  let mut count = n
  loop count {
    _..<0 => break
    _ => count = count - 1
  }
  return count
}

Suggestion

Either add a continue statement if you need to restart the loop:

fn countdown(n : Int) -> Int {
  let mut count = n
  loop count {
    _..<0 => break
    _ => {
      continue count - 1
    }
  }
  return count
}

Or use if/match you don't need to use continue:

fn countdown(n : Int) -> Int {
  let mut count = n
  match count {
    _..<0 => ()
    _ => count = count - 1
  }
  return count
}