E4121

E4121#

The attribute (!, ?, !! mark) cannot be used on this application.

This error occurs when:

  • The attribute (!, ?, !! mark) is used on a constructor.

  • The attribute is used on a function that does not fit.

    • ! must be used only on an application that raises or is async.

    • !! must be used only on an async application.

Erroneous example#

///|
pub enum Err {
  IntErr(Int)
}

///|
fn square(x : Int) -> Int {
  x * x
}

///|
pub fn invalid_attribute() -> Unit {
  square!!(1) |> ignore()
  // Error: The attribute `!!` cannot be used on application that does not raise
  // errors.
}

Suggestion#

Remove the attribute (!, ?, !! mark) from the application.

///|
pub enum Err {
  IntErr(Int)
}

///|
fn square(x : Int) -> Int {
  x * x
}

///|
pub fn constructor_value() -> Err {
  IntErr(1)
}

///|
pub fn square_value() -> Int {
  square(2)
}
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