get_char/1 panic

[flexoron]

v0.9.4-286-g00e6e323

$ scryer-prolog -f
?- get_char(A).
a
   A = a.
?- get_char(a).
a
   true.
?- get_char(End_of_file).
^D
   End_of_file = end_of_file.
?- get_char(end_of_file).
^D
thread 'main' panicked at src/machine/system_calls.rs:3469:50:
called `Option::unwrap()` on a `None` value
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
$

[UWN]

even

?- get_char(end_of_file).
a
thread 'main' panicked at src/machine/system_calls.rs:3485:50:
called `Option::unwrap()` on a `None` value

in other words:

?- get_char(end_of_file).
   inputs("a"),
   false. % expected, but not found

However,

?- open('/dev/null',read,S),get_char(S,end_of_file).
   S = '$stream'(0x638d31165ea0).
?- open('/dev/null',read,S),get_char(S,end_of_file),close(S).
   S = '$dropped_value'.

[flexoron]

On the side, get_single_char/1 behaves different. Are these results below expected?

?- use_module(library(charsio)). 
   true.

?- get_single_char(C). % Ctrl-D pressed 
   C = d. % unexpected

?- get_single_char(Char). % Ctrl-Shift-D pressed
   Char = d. % why not 'D' ?

?- get_single_char(Char). % Shift-D
   Char = 'D'. % expected

Question: Ctrl key is generally ineffective? Except Ctrl-C, Ctrl-M and (Toplevel) Ctrl-J.

?- get_single_char(Char). % Instead of <Return>, press Ctr-M Ctrl-M 
   Char = '\n'.
?- get_single_char(Char). % Ctrl-J Ctrl-M
   Char = '\n'.
?- get_single_char(Char). % Ctrl-J Ctrl-J
   Char = j. % Ctrl-J is ignored but behaves like <Return> or Ctrl-M (at the toplevel). 

?- get_char(Char). % Ctrl-J Ctrl-J

   Char = '\n'.
?- 

[bakaq]

The Ctrl key is used in the terminal to send special terminal codes, which can be detected and identified but which do not interact with the Shift key, so the combination Ctrl+Shift is kind of useless in the terminal because it will send the same code as with just Ctrl. That's why you won't see Ctrl+Shift being used in Vim, and probably part of the reason Emacs users (which use A LOT of modifiers) prefer the GUI.

I don't think it's the role of get_char/1 or get_single_char/1 to get modifiers (Ctrl, Alt), but we probably should present some way to do that eventually.

[flexoron]

Useless?
Ctrl-C = SIGINT
Ctrl-Shift-C = Copy text

[bakaq]

Ctrl-Shift-C doesn't get passed to applications, is just what most terminals use to copy text. Notice that it's the terminal that does the work in this case, and the application doesn't get anything.

[flexoron]

A keyboard is attached to the kernel who provides scancodes.
So, I guess, a detached application can open /dev/input/event5 (perhaps the keyboard)?.

Another example how scryer reacts on a Ctrl key:

$ scryer-prolog -f
?- use_module(library(charsio)).
   true.
?- get_single_char(C). % Ctrl-Z
   C = z.
?- halt.
but
$ scryer-prolog -f
?- get_char(C). % Ctrl-Z

[1]+  Stopped                 scryer-prolog -f
$

I know what you talking about, so don't let us discuss it.
The point is that I get different results( get_char, get_single_char)
and the question is why do we need it and for what?
And let me say in case of ^M (get_single_char/1)
I expect 'm' and not '\n' or the other way around for ^J expecting '\n' and not 'j'.

[flexoron]

Here is another issue:
?- get_char(C).%comment
C = '%'.
?-
#2795

[UWN]

Please do not mix so many different aspects into one single issue. The only effect is that this issue will then never be closed, because of some entirely unrelated thing.

[flexoron]

Replaced! #2797