From: Eli Zaretskii <eliz@gnu.org>
To: phillip.lord@russet.org.uk (Phillip Lord)
Cc: emacs-devel@gnu.org
Subject: Re: standard output/error/input streams
Date: Sat, 14 Jan 2017 16:31:54 +0200 [thread overview]
Message-ID: <838tqdbtlx.fsf@gnu.org> (raw)
In-Reply-To: <87wpdxu8yt.fsf@russet.org.uk> (phillip.lord@russet.org.uk)
> From: phillip.lord@russet.org.uk (Phillip Lord)
> Date: Sat, 14 Jan 2017 12:22:50 +0000
>
> I've worked up the patch that I made to add input streams for writing to
> the system standard out. There was some discussion about this in Jul.
>
> https://lists.gnu.org/archive/html/emacs-devel/2016-07/msg00910.html
>
> The new version is on feature/stdout-stderr-stream.
Thanks. Some of the concerns I expressed here:
https://lists.gnu.org/archive/html/emacs-devel/2016-07/msg00938.html
are still relevant, and at the very least should be reflected in the
docs.
> Can I add this to master?
I think this still "needs work", see my comments below:
+@cindex @code{external-standard-input}
+@defun external-standard-input &optional char
No need to explicitly index a function that is introduced in a @defun:
the latter automatically adds an index entry.
+This function reads a single character from the system standard input
+(as opposed to @var{standard-input}) and functions as a stream. Note,
Two spaces between sentences, please (here and elsewhere).
+however, that if Emacs is running in a terminal its use can be
+unpredictable.
I think we should explain more about the issue here, so that the
reader understands what she is up against. (I think this function
will simply not work on a TTY frame.)
+These functions are predominately useful for debugging, as they are a
+mechanism for producing output that does not change any buffer. Note,
+however, that if Emacs is running in a terminal their use can affect
+the display unpredictably.
Likewise here. This should also mention the problems with
stdout/stderr disposition in GUI sessions.
+(defvar external-standard-input-pushback nil
+ "Pushback character for `external-standard-input'.")
Isn't this an internal variable? If so, it should use double hyphen
in its name. And what is the purpose of this pushback? I didn't see
any code that sets it in patch.
+DEFUN ("external-standard-input-read-char",Fexternal_standard_input_read_char, Sexternal_standard_input_read_char, 0, 0, 0,
+ doc: /* Read a single character from the system standard input.
+
+Returns -1 if standard input is at the end.*/)
+ (void)
+{
+ int c;
+ Lisp_Object val;
+
+ c = getchar();
+ XSETINT(val,c);
+
+ return val;
+}
This implementation has a number of issues:
. getchar reads a _byte_, not a character, so unless input is
plain-ASCII, what you return here is a raw byte, not a character
in the Emacs sense of that word. That is inconsistent with every
other input facility we have, and could very well get the user in
trouble.
. getchar doesn't return until you type RET, at least on my system,
which might come as a surprise to users.
. (nitpicking) our coding style keeps one space between the
function/macro name and the opening parenthesis. (Same issue
exists elsewhere in the patch.)
+DEFUN ("external-standard-input-read-line", Fexternal_standard_input_read_line, Sexternal_standard_input_read_line, 0, 0, 0,
+ doc: /* Read a line from the system standard input.*/)
This function doesn't seem to be documented in the ELisp manual.
+ if (len || c == '\n' || c == '\r')
+ {
+ val = make_string (line, len);
+ xfree (line);
What about EOL decoding, as in all the other Emacs input functions?
Also, make_string has its own ideas about when to produce unibyte
strings and when multibyte strings. You should instead decode the
input text using coding-system-for-read (if non-nil) or
locale-coding-system (or maybe what terminal-coding-system returns).
+DEFUN ("external-standard-output", Fexternal_standard_output, Sexternal_standard_output, 1, 1, 0,
+ doc: /* Output character CHARACTER to system standard output. */)
+ (Lisp_Object character)
+{
+ CHECK_NUMBER (character);
+ printchar_to_stream (XINT(character), stdout);
printchar_to_stream converts the output text via
standard-display-table, if that is non-nil; do we really want that for
functionality that is supposed to be a debugging aid? It also sends
its argument to the debugger on MS-Windows -- is that desirable?
next prev parent reply other threads:[~2017-01-14 14:31 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-14 12:22 standard output/error/input streams Phillip Lord
2017-01-14 14:03 ` Noam Postavsky
2017-01-14 14:31 ` Eli Zaretskii [this message]
2017-01-14 17:51 ` Eli Zaretskii
2017-01-19 7:21 ` John Wiegley
2017-01-20 13:38 ` Phillip Lord
2017-01-20 16:26 ` Stefan Monnier
2017-01-20 21:24 ` John Wiegley
2017-01-20 21:52 ` Stefan Monnier
2017-01-20 21:59 ` John Wiegley
2017-01-23 12:41 ` Phillip Lord
2017-01-23 13:11 ` Stefan Monnier
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