make-two-way-stream input-stream output-stream => two-way-stream
two-way-stream---a two-way stream.
Returns a two-way stream that gets its input from input-stream and sends its output to output-stream.
(with-output-to-string (out) (with-input-from-string (in "input...") (let ((two (make-two-way-stream in out))) (format two "output...") (setq what-is-read (read two))))) => "output..." what-is-read => INPUT...
Should signal an error of type type-error if input-stream is not an input stream. Should signal an error of type type-error if output-stream is not an output stream.