waters@oracle.DEC (Greg Waters, 225-4986, HLO2-1/J12) (03/11/86)
> ESC is used in the Unix ... screen editor 'vi' ... > Yet, vi is quite capable of understanding special-key sequences beginning > with ESC, even though hitting ESC in command mode by itself just sounds the > bell.... vi waits for a short period after getting an ESC to see what else > it gets right afterward. If the ESC was immediately followed by the rest of > a special-key sequence, vi obeys it. > >| dan levy | yvel nad | Path: ..!{akgua,homxb,ihnp4,ltuxa,mvuxa, >| at&t computer systems division | vax135}!ttrdc!levy Obviously, this only works if the terminal is connected directly to the computer. Put a stat mux in the way, and all bets are off. Note that this vi does something harmless with what it THINKS is a lone escape. So, the problem isn't solved at all -- a lone <ESC> still can't be reliably used as a meaningful command. What does this vi do when <ESC> arrives, the timer expires, and then the rest of a valid escape sequence comes in? Interpret the sequence without the escape, or beep AND interpret the ANSI sequence? And now my question. The life of lone escapes can indeed be extended using timer hacks. All senders of information would have to encode lone escapes as <ESC> <a-time-gap>, and all direct receivers would have to implement a timer as this vi has. (This protocol comes for free when the system is a terminal connected by hard line to a computer. Well, until you turn on flow control, anyway.) Every non-real-time part of the system has to have an ANSI switch, which enables these timers and the special <ESC> treatment. Obviously, this business of using lone escapes in an ANSI environment is a KLUDGE, but it does offer the possibility of reasonable support for existing software (such as normal EMACS with hardware flow control). I know that many of my company's current products do implement special treatment for ANSI sequences, whenever there's a way to communicate the switch setting through the parts of the system. What about the rest of the market? Whose stat. muxes, TIPs, terminal networks, etc. try to keep lone escapes straight? Thanks in advance for the info, which should be posted to net.dcom (or a suitable ARPAnet list) ONLY. (N.B. My stand on this issue is compatible with my employer's. However, this posting DOES NOT and was not meant to express an opinion on the issue, whether mine or that of DEC.) Greg Waters -- DEC Hudson, MA UUCP: {...|decvax|...}!decwrl!dec-rhea!dec-oracle!waters ARPA: waters%oracle.DEC@DECWRL.ARPA