commons demo {
  type Subject = String where NonEmpty

  -- v0.43: interpolation holes — a refined String, a base Int, and a
  -- literal `$`/backtick in the surrounding text (must escape in emission).
  fn greeting(subject: Subject, count: Int) -> String {
    "Hello, \(subject)! You are visitor #\(count) — cost $0 `free`."
  }
}
