^O in EMACS


Barry Shein (encore!pinocchio!bzs@talcott.harvard.edu)
Fri, 4 Nov 88 23:28:37 est


From: mcc@ETN-WLV.EATON.COM (Merton Campbell Crockett)
>Thanks to everyone who responded and informed me the function of ^O; however,
>the question was more specifically "why?". In a rhetorical vein, why does
>EMACS, in general, use standard control characters as application dependent
>function characters? Why would any application?

On the system EMACS was developed (ITS) ^O was not a "standard control
character", at least not in the way you seem to think of it, flushing
output. I am sure one motivation for moving it with its (ITS?)
original commands to other systems was to make life easier for users
moving to those systems. EMACS was originally written in TECO, an
editor which could parse and run line noise in useful and mysterious
ways.

So, backwards compatability is one reason.

Another was mnemonic value (^O == Open Line.)

Another is it's not clear that there was ever any strong motivation to
preserve or interpret meaning for characters oriented towards line
mode when in a full-screen editor. Full-screen editors like EMACS
tended to grab the full character set (in fact, Emacs grabbed more
than the full character set, 9-bits.)

Another is that ^O is SHIFT-IN in ASCII, which means to change
character sets or some such thing, is that what you had in mind as a
more correct interpretation? It might be its use as flush output
which is questionable.

Better: Control-O on Emacs was not intended to be, particularly, ASCII
0xF. There was an intention in the original design to use other
extended character sets and Control would be just another prefix bit,
quite unlike the common usage we all know and love.

If none of this is satisfying perhaps you can suggest what you are
looking for as an explanation.

        -Barry Shein, ||Encore||



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