ensuringArgumentIsOutputChannel
fun <C : ExecutionContext> Solve.Request<C>.ensuringArgumentIsOutputChannel(index: Int): OutputChannel<String>
Same as ensuringArgumentIsChannel, additionally requiring the resolved channel to be an OutputChannel, as required by predicates writing to a stream (e.g. put_char/2, write/2).
Throws
(stream_type) if the channel resolves to an InputChannel instead.