SWI-Prolog provides (currently limited) support for localized
applications.
- The predicates char_type/2
and code_type/2
query character classes depending on the locale.
- The predicates collation_key/2
and locale_sort/2
can be used for locale dependent sorting of atoms.
- The predicate format_time/3
can be used to format time and date representations, where some of the
specifiers are locale dependent.
- The predicate format/2
provides locale-specific formatting of numbers. This functionality is
based on a more fine-grained localization model that is the subject of
this section.
A locale is a (optionally named) read-only object that provides
information to locale specific functions.120The
locale interface described in this section and its effect on format/2
and reading integers from digit groups was discussed on the SWI-Prolog
mailinglist. Most input in this discussion is from Ulrich Neumerkel and
Richard O'Keefe. The predicates in this section were designed by Jan
Wielemaker. The system creates a default locale object
named
default from the system locale. This locale is used as the
initial locale for the three standard streams as well as the
main thread. Locale sensitive output predicates such as format/3
get their locale from the stream to which they deliver their output. New
streams get their locale from the thread that created the stream.
Threads get their locale from the thread that created them.
- locale_create(-Locale,
+Default, +Options)
- Create a new locale object. Default is either an existing
locale or a string that denotes the name of a locale provided by the
system, such as
"en_EN.UTF-8". The values read from the
default locale can be modified using Options. Options
provided are:
- alias(+Atom)
- Give the locale a name.
- decimal_point(+Atom)
- Specify the decimal point to use.
- thousands_sep(+Atom)
- Specify the string that delimits digit groups. Only effective is
grouping
is also specified.
- grouping(+List)
- Specify the grouping of digits. Groups are created from the right (least
significant) digits, left of the decimal point. List is a
list of integers, specifying the number of digits in each group,
counting from the right. If the last element is
repeat(Count),
the remaining digits are grouped in groups of size Count. If
the last element is a normal integer, digits further to the left are not
grouped.
For example, the English locale uses
[ decimal_point('.'), thousands_sep(','), grouping([repeat(3)]) ]
Named locales exists until they are destroyed using locale_destroy/1
and they are no longer referenced. Unnamed locales are subject to (atom)
garbage collection.
- locale_destroy(+Locale)
- Destroy a locale. If the locale is named, this removes the name
association from the locale, after which the locale is left to be
reclaimed by garbage collection.
- locale_property(?Locale,
?Property)
- True when Locale has Property. Properties are the
same as the Options described with locale_create/3.
- set_locale(+Locale)
- Set the default locale for the current thread, as well as the locale for
the standard streams (
user_input, user_output,
user_error, current_output and current_input.
This locale is used for new streams, unless overruled using the
locale(Locale) option of open/4
or set_stream/2.
- current_locale(-Locale)
- True when Locale is the locale of the calling thread.
