Esc-F1 in menu inserts string 'OP' into buffer about ne HOT 6 CLOSED

A GUI editor can receive "events" from the GUI, so it can tell that a user hit a key with or without these modifiers (left or right shift, alt, "Win", ctrl, etc.) at a particular timestamp, followed by another and another and another.

A terminal editor does not see keystrokes. It sees instead a stream of bytes arriving at irregular intervals. When you hit F1 for example, an "escape sequence" is generated, i.e. a stream of bytes starting with Esc and followed by, in this case "O" and "P". F1 generates Esc, "O", and "Q" on my system. Ctrl-F1 generates Esc, "[", "1", ";", "5", and "P".

The thing is, except for the timing, there's no clue as to whether I hit "Ctrl-F1" or "Esc" followed by the keys "[", "1", ";", "5", and "P".

In the case you're describing, ne is seeing Esc, Esc, "O", and "P". Is that four separate keystrokes, or Esc followed by F1? There's no way to know. One thing that is known, though, is that no defined escape sequences contain escapes anywhere but at the beginning. Ne sees the first Esc, then waits up to the default EscapeTime/10 seconds (see "Help EscapeTime") for the rest of the escape sequence to come in. You throw Esc, "O" and "P" into the stream, and ne sees the 2nd Esc and figures you hit Esc twice (which is what people use instead of F1when they can't use F1 for other reasons to bring up the menu).

I'm going to stop typing now, but this is why we can't distinguish between, say, left and right ctrl keys on stream input: we can't see any modifier keys, just bytes.

Does that help?

from ne.

There's no way to avoid that. There's no way to know whether you genuinely hit ESC twice to exit the menus, and then wrote "OP", or if you hit ESC and F1.

from ne.

@vigna Can you elaborate, just so that I understand what happens here?

from ne.

@utoddl Yeah, it’s clear now, thanks. Am I right that this could have been avoided if ESC is not allowed anywhere except as the first character of an escape sequence, i.e. if ESC, ESC is not defined? If so, is there some particular reasoning for using it, or was it just a mistake?

from ne.

We're spoiled by our fancy 101+ key keyboards, but not all terminals are so blessed. The ADM3a terminal I started on had NO function keys. Esc was it. A user on such a terminal can hit Esc and wait for EscapeTimeout/10 seconds -- or hit Esc twice -- to get a menu. Given the problem, I think the double-Esc is a pretty good choice.

Is there a compelling need to hit Esc-F1 while in a menu? Even with boxing gloves on, StrongBad can hit single keys. Hit Esc twice. Or hit F1. You'll be happier.

from ne.

Well, on a limited terminal the user could – as a last resort – manually enter the sequence with which there’s no key associated or maybe a sequence defined by ne specifically for this purpose.

There’s no need really, I must have hit them by accident, and I was wondering if it was a bug, and if not, what’s the underlying reason. At this point I’m just trying to understand the design decisions ne took.

from ne.