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Re: Issue PEEK-CHAR-READ-CHAR-ECHO
- To: cl-cleanup@SAIL.STANFORD.EDU
- Subject: Re: Issue PEEK-CHAR-READ-CHAR-ECHO
- From: "Steve Bacher (Batchman)" <SEB1525@draper.com>
- Date: Tue, 14 Mar 89 08:19 EST
> From: "Kim A. Barrett" <IIM%ECLA@eclc.usc.EDU>
> Subject: Issue PEEK-CHAR-READ-CHAR-ECHO
> To: kmp@scrc-stony-brook.ARPA
> Cc: email@example.com.EDU, iim%ECLA@eclc.usc.EDU
> 1. Define two operations on streams, ECHO and UNECHO.
> 2. echo-streams, when reading a character, apply echo to the output stream and
> the character. unread on echo-streams calls unecho on the output stream
> and char, in addition to passing along the unread to the input stream.
> 3. Other meta-streams simply pass these operations along to their output side.
> 4. data-streams have two choices, depending on whether they have the
> capability to 'back out' output. If they can back it out, then echo is
> equivilent to write-char, and unecho backs it out. If they can't, then
> they record the echo in a slot, writing any already pending echo. unecho
> clears the pending echo slot. all normal output operations first write
> pending echo. a normal close also forces pending echoing.
> There is potentially more hair involved, intended to either support or
> complain about improper usage, like calling unread after peek, doing output
> between the read and the unread, &etc. Note that this depends on the single
> unread restriction in order to work right in all cases.
There SURE IS more hair involved. All you're doing is punting the basic
problem down to a lower level. Maybe the stream internally takes the actual
send-the-character-to-the-output-stream and implements it via SEND-OUT and
UN-SEND-OUT calls, where SEND-OUT buffers the character in case an UN-SEND-OUT
'foo(* a b)
example, when the ( is seen, either it gets echoed at that point or it
doesn't. This ECHO/UNECHO stuff doesn't change anything. And posing a
restriction on stream output between READ and UNREAD is unreasonable,
in my opinion.