LC_NUMERIC formatting [FEATURE REQUEST]

LC_NUMERIC formatting [FEATURE REQUEST]

[Boruch Baum]

Please consider having the elisp 'format' function adopt the
single-quote and 'I' flags. Each is already implemented in both the GNU
C printf command and the linux printf command. The single-quote flag is
part of the 'Single UNIX Specification' and the 'I' flag has been part
of glibc since version 2.2 [ref: man(3) printf].

If function 'format' uses 'printf' as its backend, this would seem to be
a matter of exposing an existing feature.

The single-quote flag applies a locale's thousands' grouping characters
if appropriate, which I only find currently implemented as user-defined
functions, ie. outside of emacs-core.

   $ printf "%'d\n" 1234
   1,234

The 'I' flag [from man(3) printf]:

   uses the locale's alternative output digits, if any. For example,
   since glibc 2.2.3 this will give Arabic-Indic digits in the Persian
   ("fa_IR") locale.

   $ LC_ALL=fa_IR.utf8 /usr/bin/printf "%Id\n" 1234
   ۱۲۳۴
   $ LC_ALL=fa_IR.utf8 /usr/bin/printf "%'Id\n" 1234
   ۱٬۲۳۴

--
hkp://keys.gnupg.net
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CSV parsing and other issues (Re: LC_NUMERIC)

[Maxim Nikulin]

On 03/06/2021 01:54, Boruch Baum wrote:
> Please consider having the elisp 'format' function adopt the
> single-quote and 'I' flags. Each is already implemented in both the GNU
> C printf command and the linux printf command. The single-quote flag is
> part of the 'Single UNIX Specification' and the 'I' flag has been part
> of glibc since version 2.2 [ref: man(3) printf].
> 
> If function 'format' uses 'printf' as its backend, this would seem to be
> a matter of exposing an existing feature.

I do not know the story why Emacs does not support locale-aware number 
formats, but I suspect that relying on libc is opening a can of worms. 
Once setlocale(LC_NUMERIC, "") is invoked, one is never sure if printf- 
and scanf-like functions deal with default "C" representation or with 
formatted accordingly to current locale numbers. Some numbers related to 
communication protocols must be always formatted using "C" locale. I do 
not remember if it happened with XFree86 or with Xorg, but at certain 
moment users experienced problems. X11 could not start at all due to 
invalid configs. The source of problem was "," as decimal separator in 
some locales and wrong expectations concerning numbers in config files.

Recently I found the following fixup_locale function:
http://git.savannah.gnu.org/cgit/emacs.git/tree/src/emacs.c#n2861

     setlocale (LC_NUMERIC, "C");

I was surprised that impossible to determine current decimal separator 
from elisp. At the same time e.g. `string-collate-lessp' has LOCALE 
argument.

A month ago some patches were submitted to Org mode with intention to 
improve import of tables, see https://debbugs.gnu.org/47885 A part of 
discussion is missed in the bug tracker: 
https://lists.gnu.org/archive/html/emacs-orgmode/2021-05/msg00693.html 
Org mode has a piece of code that tries to guess if the file has commas 
or tabs as field separator (CSV or TSV format). The suggested change 
adds e.g. semicolon. (Sidenote: probably csv-mode is a better place than 
org-mode for such code.)

The problem is that office software uses semicolon for locales where 
comma serves as decimal separator for floating-point numbers (e.g. 
de_DE, es_ES, fr_FR, ru_RU, etc.):

     A;1,2;3,4

So semicolon should be tried with higher priority than comma if in 
current locale numbers are represented as e.g 1,2. Unfortunately the 
only way to get such information from Emacs is to call some external 
application. Maintaining own mapping of locale to separator is 
unnecessary burden.

Besides office software, there are some equipment that always use "C" 
number formatting, so a user can have a mix of files with various 
dialects of CSV. Thus locale info is not enough, some heuristics is 
required anyway.

More subtle questions rise on the next step. Org allows to perform 
calculations on table cells (and there is calc). Should numbers be 
converted to "C" locale representation during import? Should conversion 
happen when passing cell content as argument and the result converted 
back to current locale? I anticipate that buffer-local setting will be 
requested. There was even discussion of mixed-language documents in 
emacs-orgmode mail list, however numbers were not mentioned.

So locale-aware number formatting would be a great improvement for 
Emacs. On the other hand, it should be implemented with great care to 
avoid localized numbers in some cases. Maybe locale argument should be 
passed to functions that deal with numbers. Formatting of integer 
numbers is not enough, floating point numbers should be handled as well. 
Parsing numbers formatted accordingly to locale rules should be 
addressed too. A function similar to `locale-info' is highly desired to 
get properties of locale (e.g. decimal_point from result of localeconv). 
Some decision is required whether calc & Co should operate with
localized numbers.

Re: CSV parsing and other issues (Re: LC_NUMERIC)

[Eli Zaretskii]

> From: Maxim Nikulin <manikulin@gmail.com>
> Date: Thu, 3 Jun 2021 21:44:08 +0700
> Cc: Utkarsh Singh <utkarsh190601@gmail.com>
> 
> So locale-aware number formatting would be a great improvement for 
> Emacs. On the other hand, it should be implemented with great care to 
> avoid localized numbers in some cases. Maybe locale argument should be 
> passed to functions that deal with numbers. Formatting of integer 
> numbers is not enough, floating point numbers should be handled as well. 
> Parsing numbers formatted accordingly to locale rules should be 
> addressed too. A function similar to `locale-info' is highly desired to 
> get properties of locale (e.g. decimal_point from result of localeconv). 
> Some decision is required whether calc & Co should operate with
> localized numbers.

Setting a locale globally in Emacs is a non-starter, for the reasons
that you point out and others.  Text processing in Emacs is generally
separate from the current locale's rules, mainly to have Emacs work
the same in any locale.  So passing a locale argument to functions
that produce output, with the intent to request some behavior to be
tailored to that locale, is the only reasonable way to have this kind
of functionalities in Emacs.  The problem with that, of course, is
that not every supported platform can dynamically change the locale,
let alone do that efficiently.

Re: CSV parsing and other issues (Re: LC_NUMERIC)

[Maxim Nikulin]

On 03/06/2021 22:01, Eli Zaretskii wrote:
>> From: Maxim Nikulin
>> Date: Thu, 3 Jun 2021 21:44:08 +0700
>>
>> So locale-aware number formatting would be a great improvement for
>> Emacs. On the other hand, it should be implemented with great care to
>> avoid localized numbers in some cases. Maybe locale argument should be
>> passed to functions that deal with numbers. Formatting of integer
>> numbers is not enough, floating point numbers should be handled as well.
>> Parsing numbers formatted accordingly to locale rules should be
>> addressed too. A function similar to `locale-info' is highly desired to
>> get properties of locale (e.g. decimal_point from result of localeconv).
>> Some decision is required whether calc & Co should operate with
>> localized numbers.
> 
> Setting a locale globally in Emacs is a non-starter, for the reasons
> that you point out and others.  Text processing in Emacs is generally
> separate from the current locale's rules, mainly to have Emacs work
> the same in any locale.  So passing a locale argument to functions
> that produce output, with the intent to request some behavior to be
> tailored to that locale, is the only reasonable way to have this kind
> of functionalities in Emacs.  The problem with that, of course, is
> that not every supported platform can dynamically change the locale,
> let alone do that efficiently.

I do not think it is efficient to require from users to fight with 
number formatting themselves. Some links from my browser history when I 
was trying to figure out how to get locale-specific decimal separator in 
elisp:

https://stackoverflow.com/questions/35661173/how-to-format-table-fields-as-currency-in-org-mode
https://www.emacswiki.org/emacs/AddCommasToNumbers
https://www.reddit.com/r/emacs/comments/61mhyx/creating_a_function_to_add_commasseparators_to/

Do you mean that it is necessary to create new implementation of number 
formatter specially for Emacs? Something like

https://unicode.org/reports/tr35/tr35-numbers.html
Unicode Locale Data Markup Language (LDML) Part 3: Numbers

Actually it is an almost random link. I do not know which source is 
currently considered as the best collection of wisdom related to number 
formatting. Outside of Emacs world, when I needed numbers formatted 
accordingly to various locales previous time, I was lucky enough to use 
code similar to the following one and did not care concerning details:

#include <cstdio>
#include <QLocale>
#include <QTextStream>

void test(QTextStream& stream, const char *loc_name) {
	QLocale loc(QString::fromLocal8Bit(loc_name));
	stream << "point: " << loc.decimalPoint()
		<< " " << loc.toString(12345.67)
		<< " " << loc.toString(1234567890) << "\n";
}
int main(int argc, char *argv[]) {
	QTextStream stream(stdout);
	for (int i = 1; i < argc; ++i) {
		test(stream, argv[i]);
	}
	return 0;
}

./qtloc de_DE en_GB fa_IR
point: , 12.345,7 1.234.567.890
point: . 12,345.7 1,234,567,890
point: ٫ ۱۲٬۳۴۵٫۷ ۱٬۲۳۴٬۵۶۷٬۸۹۰

Surprisingly it works even despite I have not generated de and fa locales.

On linux I see that Emacs is linked with ICU

ldd /usr/bin/emacs | grep -i icu
	libicuuc.so.66 => /usr/lib/x86_64-linux-gnu/libicuuc.so.66 
(0x00007f457c799000)
	libicudata.so.66 => /usr/lib/x86_64-linux-gnu/libicudata.so.66 
(0x00007f457a61c000)

I am not familiar with ICU API but I expect that it may be utilized
https://github.com/unicode-org/icu/blob/main/icu4c/source/samples/numfmt/capi.c

Do you have a bright idea concerning implementation of parser-formatter 
for numbers with reasonable efforts?

Re: CSV parsing and other issues (Re: LC_NUMERIC)

[Eli Zaretskii]

> Cc: utkarsh190601@gmail.com
> From: Maxim Nikulin <manikulin@gmail.com>
> Date: Fri, 4 Jun 2021 23:31:13 +0700
> 
> > Setting a locale globally in Emacs is a non-starter, for the reasons
> > that you point out and others.  Text processing in Emacs is generally
> > separate from the current locale's rules, mainly to have Emacs work
> > the same in any locale.  So passing a locale argument to functions
> > that produce output, with the intent to request some behavior to be
> > tailored to that locale, is the only reasonable way to have this kind
> > of functionalities in Emacs.  The problem with that, of course, is
> > that not every supported platform can dynamically change the locale,
> > let alone do that efficiently.
> 
> I do not think it is efficient to require from users to fight with 
> number formatting themselves.

I didn't suggest that.  I was talking about the design of the APIs
that need to be able to provide locale-specific formatting.  The
implementation should be provided by Emacs core, of course.

> Do you mean that it is necessary to create new implementation of number 
> formatter specially for Emacs?

Either that, or use the underlying C library if it can accept a locale
specifier, or if it supports efficient dynamic change of the locale,
like we do in some of the implementations of string-collate-lessp.

> On linux I see that Emacs is linked with ICU

It isn't.  It's either HarfBuzz or maybe libc that pulls in the ICU
library.  Emacs doesn't use it directly.

> Do you have a bright idea concerning implementation of parser-formatter 
> for numbers with reasonable efforts?

See above.