Lykn

switch

(switch status
  (200 (process-ok) (break))
  (404 (not-found) (break))
  (500 (server-error) (break))
  (default (unknown-status status)))

switch (status) {
  case 200: processOk(); break;
  case 404: notFound(); break;
  case 500: serverError(); break;
  default: unknownStatus(status);
}

The Syntax

(switch expr (case-value body...) ... (default body...)). Each case is a parenthesized group: the first element is the test value, the rest is the body. default handles the fallback.

Explicit break

Lykn’s switch does not auto-break. Each case needs an explicit (break) to prevent fallthrough — the same as JavaScript. If you want fallthrough (rare), omit the break.

But Consider match

switch has no exhaustiveness checking. If you add a new status code and forget to add a case, the default branch runs silently — or worse, if there’s no default, nothing runs at all.

match (Chapter 10) catches missing cases at compile time. For dispatching on tagged data types, match is strictly better. Use switch when the value is an open type (arbitrary status codes, string commands) where a default fallback is the correct behaviour.