type Result { Done
 error Failed(message: Text) }

type Message { Value(value: Int?) }

produce(values: Channel<Int>) () { send(values, 10)
 send(values, 20)
 close(values) }

handled(value: null) (answer: Bool) recover("处理接收错误") { answer = false }
handled(value: Result.Done) (answer: Bool) recover("处理接收错误") { answer = false }
handled(value: Result.Failed(message)) (answer: Bool) recover("处理接收错误") { answer = message == "reason" }

nested(value: null) (answer: Bool) { answer = false }
nested(value: Channel<Int>) (answer: Bool) { answer = receive(value) == 7 }

verify() (answer: Bool) {
 values = channel(Int, 1)
 pending = run(produce(values))
 first = receive(values)
 second = receive(values)
 end = receive(values)
 wait(pending)
 nullable_values = channel(Message, 2)
 send(nullable_values, Message.Value(null))
 send(nullable_values, Message.Value(30))
 nullable_item = receive(nullable_values)
 present = receive(nullable_values)
 alias = nullable_values
 close(alias)
 nullable_end = receive(nullable_values)
 lists = channel(List<Int>, 1)
 original = [1, 2]
 send(lists, original)
 original = append(original, 3)
 copied = receive(lists)
 nested_values = channel(Channel<Int>, 1)
 child = channel(Int, 1)
 send(child, 7)
 send(nested_values, child)
 nested_ok = nested(receive(nested_values))
 failures = channel(Result, 1)
 send(failures, Result.Failed("reason"))
 error_ok = handled(receive(failures))
 answer = first == 10 and second == 20 and end == null and nullable_item == Message.Value(null) and present == Message.Value(30) and nullable_end == null and copied == [1, 2] and original == [1, 2, 3] and nested_ok and error_ok
}

creation() (value: Channel<Int>) { value = channel(Int, 1) }

nullable() (value: Channel<Int>?) { value = null }

invalid() () { values = channel(Int, 0) }

closed() () { values = channel(Int, 1)
 close(values)
 send(values, 42) }