From: T. V. Raman
Subject: Duplicating the output of a serial stream: How?
Date: Sun, 04 Oct 1992 18:39:48 +0000
Message-ID: <1992Oct4.183948.5008@cs.cornell.edu>

Hi!

I have a program that opens a serial stream as a split stream and both
writes and reads from this device. I would like to write a macro that
when called will result in all output that is sent to the serial
stream by the containing forms  being dribbled to a file specified by
the user. I tried the following:

(defmacro with-file-as-well-as-dectalk ((&key (filename "temp")) &body body) 
  "Read into file instead of speaking. "
  `(let (
         (saved-stream dectalk:*stream*)
         (file-stream
          (open
           (merge-pathnames
            (user-homedir-pathname)
            ,filename )
           :direction :io
           :if-does-not-exist :create
           ))
         )
    (unwind-protect
         (progn
           (setf dectalk:*stream*
                 (make-broadcast-stream dectalk:*stream* file-stream))
           ,@body)
      (setf dectalk:*stream*
            saved-stream)
      (close file-stream)
      )
    )
  )


But the above does not work and I get an error as follows since the
broadcast stream will only allow output. How do I write the above so
that the file-stream gets connected only to the output side of the
split stream?

Is the above possible, and if so what is the clean way of doing it? 


>>Error: Stream #<Stream BROADCAST-STREAM 15F7A26> is not open for input

READ-CHAR-NO-HANG:
   Optional arg 0 (STREAM): #<Stream BROADCAST-STREAM 15F7A26>
   Optional arg 1 (EOF-ERROR-P): T
   Optional arg 2 (EOF-VALUE): NIL
   Optional arg 3 (RECURSIVEP): NIL
:A  0: Abort to Lisp Top Level

-> 
-- 
   T. V. Raman <·····@cs.cornell.edu>Tel: (607)255-9202  R 272-3649
                       Office: 4116 Upson Hall,
Department of Computer Science, Cornell University Ithaca NY 14853-6201
                Res: 226 Bryant Avenue Ithaca NY 14850

From: Barry Margolin
Subject: Re: Duplicating the output of a serial stream: How?
Date: Mon, 05 Oct 1992 14:02:47 +0000
Message-ID: <1aphu7INN6jm@early-bird.think.com>

In article <····················@cs.cornell.edu> ·····@cs.cornell.edu (T. V. Raman) writes:
>But the above does not work and I get an error as follows since the
>broadcast stream will only allow output. How do I write the above so
>that the file-stream gets connected only to the output side of the
>split stream?

Use MAKE-TWO-WAY-STREAM.  The output side of the two-way stream should be
the broadcast stream that you constructed in your original code, and the
input side should be the stream that you're duplicating.

Also, you should use WITH-OPEN-STREAM to open and close these temporary
streams rather than your own UNWIND-PROTECT.
-- 
Barry Margolin
System Manager, Thinking Machines Corp.

······@think.com          {uunet,harvard}!think!barmar