Enums
An enum is a tagged union: a fixed set of variants, each optionally carrying typed named fields. Declare it at the top level, before main.
Declaration
enum status = [
Ready,
Failed(str reason)
]{}- The variant list is
[ ... ]and the trailing{ ... }body is required; omitting it fails withexpected '{' after enum variants(use{}when empty). - A variant is either a bare name (
Ready) or a name with typed fields (Failed(str reason)). - Payload types and arity are checked when the variant is constructed.
Construction
any a = status.Ready;
any b = status.Failed("disk");A payload field is read like a record field:
println(b.reason); // diskAn enum value prints as Enum.Variant (println(a) prints status.Ready).
Matching with switch
An enum value is normally consumed with a switch pattern, which destructures the payload and binds the field names for the case body:
func describe(status value) -> str {
switch (value) {
case(status.Ready){ return "ready"; }
case(status.Failed(reason)){ return "failed: " + reason; }
}
return "unknown";
}See language for the general switch form.
Equality is identity, not structure
Enum values compare by identity, so two separately built variants are never equal — even two Readys, and even a variant compared with itself after a round trip:
println(status.Ready is status.Ready); // false
println(status.Failed("x") is status.Failed("x")); // false
any a = status.Ready;
println(a is a); // trueUse switch patterns to test which variant a value is; do not use is.
Full example
global setup(){}
enum status = [
Ready,
Failed(str reason)
]{}
func describe(status value) -> str {
switch (value) {
case(status.Ready){ return "ready"; }
case(status.Failed(reason)){ return "failed: " + reason; }
}
return "unknown";
}
global main(){
any a = status.Ready;
any b = status.Failed("disk");
println(a); // status.Ready
println(b.reason); // disk
println(describe(a)); // ready
println(describe(b)); // failed: disk
}