From: John Cowan <xxxxxx@ccil.org>
Date: Thursday, August 15, 2019 11:04 AM
I'm still thinking we should expose below these fancy procedures the system calls, struct, and flags primitives they use to get and set line disciplines.
I'm not convinced, but I'm willing to discuss it.
Perhaps your Scheme's dynamic-wind isn't so magic, or doesn't exist.
If so, the Scheme is not even R5RS-compliant. Systems that lack R5RS nowadays are toys or written for a special purpose: Scheme 9 as an illustration of how easy it is to write a cleanly coded Scheme interpreter in C, for example.
This SRFI is not demanding much in the way of magic except in this one place, right?
Your POSIX changing line discipline loses characters when switching from canonical mode, I don't think we can demand all implementations of POSIX a Scheme runs on to be perfect. The scenario I conceive of here is that between invocations of e.g. with-rare-mode a character gets in the canonical mode domain and then is "flushed" in POSIX terms, that is discarded, when we return to raw mode, despite using the NOW option for that.
All the more reason to make changes in between modes rare. A pure TUI editor would start in raw mode and stay there until it shuts down. A bimodal editor like vi switches only at well-defined points. Switching from ex to vi mode takes some time anyway, and it wouldn't occur to me to try typing ahead then.
Ummm, unless I completely misunderstand how it's to be used, which I guess I am ... I now guess that the idea of the with-raw-mode etc. functions is that after you do basic application setup, you run your application with the thunk you hand with-raw-mode or with-rare-mode.
For some reason, perhaps because they return strings, perhaps because of the description, how you can interpret the second and final sentence, I was envisioning you'd call them for each small set of characters you'd be getting from the user.
Perhaps drop the string return from with-raw-mode and with-rare-mode? The without-echo should return after a password, pass phrase or the like has been entered with an ending newline, haven't yet groked the purpose of without-interrupt-chars.
If my new understanding is correct, much of this can be addressed with more thorough documentation.
Your POSIX line discipline doesn't allow setting everything we assume it can. For historical reasons you're actually required to get, set, which will return 0 if any of the changes are accepted, then get again to make sure all or "enough" of the changes were made. Which also brings up the question about what we should do with these procedures if that happens.
In the before-thunk, the terminal should be restored and the whole thing aborted. In the after-thunk, it's unclear; there shouldn't be any reason why restoration should fail. That's why we have exceptions.
That's what I was thinking ... except if that happens, you're stuck if you can't construct your own less capable version with the primitives I advocate exposing, unless the lack of capability is so great it's impossible.
According to ... Wikipedia, rare/cbreak mode, which I've not actually used, is for character at a time input. Does that mean with-rare-mode should hang until it gets a character, or should it (can it?) use the timeout line discipline feature that with-rare-mode uses.
Rare mode is basically raw mode except that the normal signal characters (^C, ^\, ^Z) send signals instead of being passed through.
Note that in both rare and raw mode it's actual calls to read-char that hang, just as in cooked mode, and *not* the with-*-mode wrapper.
So with-rare-mode should get the min and time arguments like with-raw-mode.
Ugh, that sounds like a horrible "feature". But I think we should allow for "magic echo", a dot per typed character, and rubout deleting the last dot. Maybe ^U the whole set of characters typed.
That can be done with a higher-level routine using with-rare-mode with a timeout of 0,
Sounds like yes to my above statement.
so it processes characters as it gets them, doing its own echoing and interpretation of rubout-like characters. (It doesn't make sense to turn off signaling in this context, which is why it should be rare and not raw.) But it doesn't need anything special beyond that IIUC.
All this is sounding quite a bit better, thanks!
- Harold