[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Does READ-CHAR echo?
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.
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 kind of assume that we all agree that READ and READ-LINE should echo
the characters as they come in from an interactive terminal. Perhaps,
we should state that explicitly in the next edition of the manual.
I believe Carl Hoffman (who wrote the Lisp Machine rubout handler) has
some thoughts on this, which I hope this letter will spur him to share with us.