guile/doc/ref/api-i18n.texi

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@c This is part of the GNU Guile Reference Manual.
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@c   Free Software Foundation, Inc.
@c See the file guile.texi for copying conditions.

@page
@node Internationalization
@section Support for Internationalization

Guile provides an interface to GNU @code{gettext} for translating
message strings (@pxref{Introduction,,, gettext, GNU @code{gettext}
utilities}).

Messages are collected in domains, so different libraries and programs
maintain different message catalogues.  The @var{domain} parameter in
the functions below is a string (it becomes part of the message
catalog filename).

When @code{gettext} is not available, or if Guile was configured
@samp{--without-nls}, dummy functions doing no translation are
provided.

@deffn {Scheme Procedure} gettext msg [domain [category]]
@deffnx {C Function} scm_gettext (msg, domain, category)
Return the translation of @var{msg} in @var{domain}.  @var{domain} is
optional and defaults to the domain set through @code{textdomain}
below.  @var{category} is optional and defaults to @code{LC_MESSAGES}
(@pxref{Locales}).

Normal usage is for @var{msg} to be a literal string.
@command{xgettext} can extract those from the source to form a message
catalogue ready for translators (@pxref{xgettext Invocation,, Invoking
the @command{xgettext} Program, gettext, GNU @code{gettext}
utilities}).

@example
(display (gettext "You are in a maze of twisty passages."))
@end example

@code{_} is a commonly used shorthand, an application can make that an
alias for @code{gettext}.  Or a library can make a definition that
uses its specific @var{domain} (so an application can change the
default without affecting the library).

@example
(define (_ msg) (gettext msg "mylibrary"))
(display (_ "File not found."))
@end example

@code{_} is also a good place to perhaps strip disambiguating extra
text from the message string, as for instance in @ref{GUI program
problems,, How to use @code{gettext} in GUI programs, gettext, GNU
@code{gettext} utilities}.
@end deffn

@deffn {Scheme Procedure} ngettext msg msgplural n [domain [category]]
@deffnx {C Function} scm_ngettext (msg, msgplural, n, domain, category)
Return the translation of @var{msg}/@var{msgplural} in @var{domain},
with a plural form chosen appropriately for the number @var{n}.
@var{domain} is optional and defaults to the domain set through
@code{textdomain} below.  @var{category} is optional and defaults to
@code{LC_MESSAGES} (@pxref{Locales}).

@var{msg} is the singular form, and @var{msgplural} the plural.  When
no translation is available, @var{msg} is used if @math{@var{n} = 1},
or @var{msgplural} otherwise.  When translated, the message catalogue
can have a different rule, and can have more than two possible forms.

As per @code{gettext} above, normal usage is for @var{msg} and
@var{msgplural} to be literal strings, since @command{xgettext} can
extract them from the source to build a message catalogue.  For
example,

@example
(define (done n)
  (format #t (ngettext "~a file processed\n"
                       "~a files processed\n" n)
             n))

(done 1) @print{} 1 file processed
(done 3) @print{} 3 files processed
@end example

It's important to use @code{ngettext} rather than plain @code{gettext}
for plurals, since the rules for singular and plural forms in English
are not the same in other languages.  Only @code{ngettext} will allow
translators to give correct forms (@pxref{Plural forms,, Additional
functions for plural forms, gettext, GNU @code{gettext} utilities}).
@end deffn

@deffn {Scheme Procedure} textdomain [domain]
@deffnx {C Function} scm_textdomain (domain)
Get or set the default gettext domain.  When called with no parameter
the current domain is returned.  When called with a parameter,
@var{domain} is set as the current domain, and that new value
returned.  For example,

@example
(textdomain "myprog")
@result{} "myprog"
@end example
@end deffn

@deffn {Scheme Procedure} bindtextdomain domain [directory]
@deffnx {C Function} scm_bindtextdomain (domain, directory)
Get or set the directory under which to find message files for
@var{domain}.  When called without a @var{directory} the current
setting is returned.  When called with a @var{directory},
@var{directory} is set for @var{domain} and that new setting returned.
For example,

@example
(bindtextdomain "myprog" "/my/tree/share/locale")
@result{} "/my/tree/share/locale"
@end example

When using Autoconf/Automake, an application should arrange for the
configured @code{localedir} to get into the program (by substituting,
or by generating a config file) and set that for its domain.  This
ensures the catalogue can be found even when installed in a
non-standard location.
@end deffn

@deffn {Scheme Procedure} bind-textdomain-codeset domain [encoding]
@deffnx {C Function} scm_bind_textdomain_codeset (domain, encoding)
Get or set the text encoding to be used by @code{gettext} for messages
from @var{domain}.  @var{encoding} is a string, the name of a coding
system, for instance @nicode{"8859_1"}.  (On a Unix/POSIX system the
@command{iconv} program can list all available encodings.)

When called without an @var{encoding} the current setting is returned,
or @code{#f} if none yet set.  When called with an @var{encoding}, it
is set for @var{domain} and that new setting returned.  For example,

@example
(bind-textdomain-codeset "myprog")
@result{} #f
(bind-textdomain-codeset "myprog" "latin-9")
@result{} "latin-9"
@end example

The encoding requested can be different from the translated data file,
messages will be recoded as necessary.  But note that when there is no
translation, @code{gettext} returns its @var{msg} unchanged, ie.@:
without any recoding.  For that reason source message strings are best
as plain ASCII.

Currently Guile has no understanding of multi-byte characters, and
string functions won't recognise character boundaries in multi-byte
strings.  An application will at least be able to pass such strings
through to some output though.  Perhaps this will change in the
future.
@end deffn

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