@_functionBuilder
struct TupleBuilder {
  static func buildBlock<T, U>(_ lhs: T, _ rhs: U) -> (T, U) { (lhs, rhs) }
}

infix operator ^^^
func ^^^ (lhs: Int, @TupleBuilder rhs: (Int) -> (String, Int)) -> (String, Int) {
  return rhs(lhs)
}

print(5 ^^^ {
  "hello"
  $0 + 1
})

main.swift:476:3: warning: string literal is unused
  "hello"
  ^~~~~~~
main.swift:477:6: warning: result of operator '+' is unused
  $0 + 1
  ~~ ^ ~
main.swift:478:1: error: missing return in a closure expected to return '(String, Int)'
})
^

func foo (_ lhs: Int, @TupleBuilder _ rhs: (Int) -> (String, Int)) -> (String, Int) {
  return rhs(lhs)
}

print(foo(5, {
  "hello"
  $0 + 1
}))