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Does READ-CHAR echo?
Date: Fri, 26 Jul 85 15:02 EDT
From: Kent M Pitman <KMP@SCRC-STONY-BROOK.ARPA>
I could not find any place in CLtL where it says whether READ-CHAR echos
the character that it has read. Likewise for PEEK-CHAR. Also, there is
no discussion of whether UNREAD-CHAR should unecho the character.
I note that Symbolics Common Lisp has (somewhat arbitrarily, I guess)
decided that READ-CHAR echos, PEEK-CHAR does not echo, and UNREAD-CHAR
does not un-echo the character. This has the odd effect that:
(PROGN (PEEK-CHAR) (UNREAD-CHAR (READ-CHAR)) (READ-CHAR))
echos the character twice. I imagine it will be a real hassle when programs
start porting if this behavior does not become standardized.
I would suggest that it is incorrect for READ-CHAR to echo a character
which was UNREAD-CHAR'd. Such a character has already been echoed once.
I think this is just a bug.
Does anyone have any thoughts about whether we should think about adding
functions called PEEK-CHAR-NO-ECHO, READ-CHAR-NO-ECHO, and UNREAD-CHAR-NO-ECHO?
Or maybe there should be WITH-INPUT-ECHO and WITHOUT-INPUT-ECHO special forms
which affect calls to the character readers within the dynamic scope of their
I think the only one needed would be READ-CHAR-NO-ECHO.