E4154

Non-constant enum with custom tag value.

MoonBit supports customizing the integer representation of constructors:

enum Flag {
  A = 1
  B = 2
  C = 3
}

However, only constant enum values (where all constructors have no payload) can have custom tags. Otherwise this error will be reported.

Erroneous example

enum Bad {
  A = 1
  B = 2
  C(Int)
}

Suggestion

Remove the payload, or remove the custom tag values:

pub enum Good {
  A = 1
  B = 2
  C = 3
}

pub fn all() -> (Good, Good, Good) {
  (A, B, C)
}