Enum design

A Norm enum is a closed algebraic data type. Each variant may carry no data or have its own field set.

enum Token {
    Number(Double value),
    Name(String text),
    End
}

Construction and type

Token.Number(value: 1.5) has static type Token, not a public subtype. A variant constructor initializes only its declared data; variants cannot be inherited or implemented separately. Explicit construction of a generic enum writes all type arguments on the type name, for example Result<Integer, Error>.Ok(value: 1). Omitting type arguments uses ordinary call-inference rules.

Matching

String describe(Token token) {
    return switch token {
        case Number(Double value) { break "number" }
        case Name(String text) { break text }
        case End { break "end" }
    }
}

The compiler recursively analyzes pattern coverage, so every switch must be exhaustive. Pattern bindings have static types and are scoped to their case block.

Evolution rules

Adding a public enum variant within the same compatibility level is a source-breaking change: existing exhaustive switches will need another case. Library authors who need an open set of extensions should use an interface instead of reserving an Unknown variant to hide model changes.

Library types such as Result<T, E> use ordinary enum definitions. They gain neither hidden control flow nor a special runtime representation.