Locale::Maketext(Perl Programmers Reference GLocale::Maketext(3p)NAMELocale::Maketext - framework for localization
SYNOPSIS
package MyProgram;
use strict;
use MyProgram::L10N;
# ...which inherits from Locale::Maketext
my $lh = MyProgram::L10N->get_handle() || die "What language?";
...
# And then any messages your program emits, like:
warn $lh->maketext( "Can't open file [_1]: [_2]\n", $f, $! );
...
DESCRIPTION
It is a common feature of applications (whether run
directly, or via the Web) for them to be "localized" --
i.e., for them to a present an English interface to an
English-speaker, a German interface to a German-speaker, and
so on for all languages it's programmed with.
Locale::Maketext is a framework for software localization;
it provides you with the tools for organizing and accessing
the bits of text and text-processing code that you need for
producing localized applications.
In order to make sense of Maketext and how all its com-
ponents fit together, you should probably go read
Locale::Maketext::TPJ13, and then read the following docu-
mentation.
You may also want to read over the source for
"File::Findgrep" and its constituent modules -- they are a
complete (if small) example application that uses Maketext.
QUICK OVERVIEW
The basic design of Locale::Maketext is object-oriented, and
Locale::Maketext is an abstract base class, from which you
derive a "project class". The project class (with a name
like "TkBocciBall::Localize", which you then use in your
module) is in turn the base class for all the "language
classes" for your project (with names
"TkBocciBall::Localize::it", "TkBocciBall::Localize::en",
"TkBocciBall::Localize::fr", etc.).
A language class is a class containing a lexicon of phrases
as class data, and possibly also some methods that are of
use in interpreting phrases in the lexicon, or otherwise
dealing with text in that language.
An object belonging to a language class is called a
"language handle"; it's typically a flyweight object.
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The normal course of action is to call:
use TkBocciBall::Localize; # the localization project class
$lh = TkBocciBall::Localize->get_handle();
# Depending on the user's locale, etc., this will
# make a language handle from among the classes available,
# and any defaults that you declare.
die "Couldn't make a language handle??" unless $lh;
From then on, you use the "maketext" function to access
entries in whatever lexicon(s) belong to the language handle
you got. So, this:
print $lh->maketext("You won!"), "\n";
...emits the right text for this language. If the object in
$lh belongs to class "TkBocciBall::Localize::fr" and
%TkBocciBall::Localize::fr::Lexicon contains "("You won!" =>
"Tu as gagne!")", then the above code happily tells the user
"Tu as gagne!".
METHODSLocale::Maketext offers a variety of methods, which fall
into three categories:
+ Methods to do with constructing language handles.
+ "maketext" and other methods to do with accessing %Lexi-
con data for a given language handle.
+ Methods that you may find it handy to use, from routines
of yours that you put in %Lexicon entries.
These are covered in the following section.
Construction Methods
These are to do with constructing a language handle:
+ $lh = YourProjClass->get_handle( ...langtags... ) || die
"lg-handle?";
This tries loading classes based on the language-tags
you give (like "("en-US", "sk", "kon", "es-MX", "ja",
"i-klingon")", and for the first class that succeeds,
returns YourProjClass::language->new().
It runs thru the entire given list of language-tags, and
finds no classes for those exact terms, it then tries
"superordinate" language classes. So if no "en-US" class
(i.e., YourProjClass::en_us) was found, nor classes for
anything else in that list, we then try its
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superordinate, "en" (i.e., YourProjClass::en), and so on
thru the other language-tags in the given list: "es".
(The other language-tags in our example list: happen to
have no superordinates.)
If none of those language-tags leads to loadable
classes, we then try classes derived from
YourProjClass->fallback_languages() and then if nothing
comes of that, we use classes named by
YourProjClass->fallback_language_classes(). Then in the
(probably quite unlikely) event that that fails, we just
return undef.
+ $lh = YourProjClass->get_handle() || die "lg-handle?";
When "get_handle" is called with an empty parameter
list, magic happens:
If "get_handle" senses that it's running in program that
was invoked as a CGI, then it tries to get language-tags
out of the environment variable "HTTP_ACCEPT_LANGUAGE",
and it pretends that those were the languages passed as
parameters to "get_handle".
Otherwise (i.e., if not a CGI), this tries various OS-
specific ways to get the language-tags for the current
locale/language, and then pretends that those were the
value(s) passed to "get_handle".
Currently this OS-specific stuff consists of looking in
the environment variables "LANG" and "LANGUAGE"; and on
MSWin machines (where those variables are typically
unused), this also tries using the module Win32::Locale
to get a language-tag for whatever language/locale is
currently selected in the "Regional Settings" (or
"International"?) Control Panel. I welcome further
suggestions for making this do the Right Thing under
other operating systems that support localization.
If you're using localization in an application that
keeps a configuration file, you might consider something
like this in your project class:
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sub get_handle_via_config {
my $class = $_[0];
my $preferred_language = $Config_settings{'language'};
my $lh;
if($preferred_language) {
$lh = $class->get_handle($chosen_language)
|| die "No language handle for \"$chosen_language\" or the like";
} else {
# Config file missing, maybe?
$lh = $class->get_handle()
|| die "Can't get a language handle";
}
return $lh;
}
+ $lh = YourProjClass::langname->new();
This constructs a language handle. You usually don't
call this directly, but instead let "get_handle" find a
language class to "use" and to then call ->new on.
+ $lh->init();
This is called by ->new to initialize newly-constructed
language handles. If you define an init method in your
class, remember that it's usually considered a good idea
to call $lh->SUPER::init in it (presumably at the begin-
ning), so that all classes get a chance to initialize a
new object however they see fit.
+ YourProjClass->fallback_languages()
"get_handle" appends the return value of this to the end
of whatever list of languages you pass "get_handle".
Unless you override this method, your project class will
inherit Locale::Maketext's "fallback_languages", which
currently returns "('i-default', 'en', 'en-US')".
("i-default" is defined in RFC 2277).
This method (by having it return the name of a
language-tag that has an existing language class) can be
used for making sure that "get_handle" will always
manage to construct a language handle (assuming your
language classes are in an appropriate @INC directory).
Or you can use the next method:
+ YourProjClass->fallback_language_classes()
"get_handle" appends the return value of this to the end
of the list of classes it will try using. Unless you
override this method, your project class will inherit
Locale::Maketext's "fallback_language_classes", which
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currently returns an empty list, "()". By setting this
to some value (namely, the name of a loadable language
class), you can be sure that "get_handle" will always
manage to construct a language handle.
The "maketext" Method
This is the most important method in Locale::Maketext:
$text = $lh->maketext(key, ...parameters for this
phrase...);
This looks in the %Lexicon of the language handle $lh and
all its superclasses, looking for an entry whose key is the
string key. Assuming such an entry is found, various things
then happen, depending on the value found:
If the value is a scalarref, the scalar is dereferenced and
returned (and any parameters are ignored). If the value is a
coderef, we return &$value($lh, ...parameters...). If the
value is a string that doesn't look like it's in Bracket
Notation, we return it (after replacing it with a scalarref,
in its %Lexicon). If the value does look like it's in
Bracket Notation, then we compile it into a sub, replace the
string in the %Lexicon with the new coderef, and then we
return &$new_sub($lh, ...parameters...).
Bracket Notation is discussed in a later section. Note that
trying to compile a string into Bracket Notation can throw
an exception if the string is not syntactically valid (say,
by not balancing brackets right.)
Also, calling &$coderef($lh, ...parameters...) can throw any
sort of exception (if, say, code in that sub tries to divide
by zero). But a very common exception occurs when you have
Bracket Notation text that says to call a method "foo", but
there is no such method. (E.g., "You have [quatn,_1,ball]."
will throw an exception on trying to call
$lh->quatn($_[1],'ball') -- you presumably meant "quant".)
"maketext" catches these exceptions, but only to make the
error message more readable, at which point it rethrows the
exception.
An exception may be thrown if key is not found in any of
$lh's %Lexicon hashes. What happens if a key is not found,
is discussed in a later section, "Controlling Lookup
Failure".
Note that you might find it useful in some cases to override
the "maketext" method with an "after method", if you want to
translate encodings, or even scripts:
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package YrProj::zh_cn; # Chinese with PRC-style glyphs
use base ('YrProj::zh_tw'); # Taiwan-style
sub maketext {
my $self = shift(@_);
my $value = $self->maketext(@_);
return Chineeze::taiwan2mainland($value);
}
Or you may want to override it with something that traps any
exceptions, if that's critical to your program:
sub maketext {
my($lh, @stuff) = @_;
my $out;
eval { $out = $lh->SUPER::maketext(@stuff) };
return $out unless $@;
...otherwise deal with the exception...
}
Other than those two situations, I don't imagine that it's
useful to override the "maketext" method. (If you run into
a situation where it is useful, I'd be interested in hearing
about it.)
$lh->fail_with or $lh->fail_with(PARAM)
$lh->failure_handler_auto
These two methods are discussed in the section "Control-
ling Lookup Failure".
Utility Methods
These are methods that you may find it handy to use, gen-
erally from %Lexicon routines of yours (whether expressed as
Bracket Notation or not).
$language->quant($number, $singular)
$language->quant($number, $singular, $plural)
$language->quant($number, $singular, $plural, $negative)
This is generally meant to be called from inside Bracket
Notation (which is discussed later), as in
"Your search matched [quant,_1,document]!"
It's for quantifying a noun (i.e., saying how much of it
there is, while giving the correct form of it). The
behavior of this method is handy for English and a few
other Western European languages, and you should over-
ride it for languages where it's not suitable. You can
feel free to read the source, but the current implemen-
tation is basically as this pseudocode describes:
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if $number is 0 and there's a $negative,
return $negative;
elsif $number is 1,
return "1 $singular";
elsif there's a $plural,
return "$number $plural";
else
return "$number " . $singular . "s";
#
# ...except that we actually call numf to
# stringify $number before returning it.
So for English (with Bracket Notation)
"...[quant,_1,file]..." is fine (for 0 it returns "0
files", for 1 it returns "1 file", and for more it
returns "2 files", etc.)
But for "directory", you'd want
"[quant,_1,directory,directories]" so that our elemen-
tary "quant" method doesn't think that the plural of
"directory" is "directorys". And you might find that
the output may sound better if you specify a negative
form, as in:
"[quant,_1,file,files,No files] matched your query.\n"
Remember to keep in mind verb agreement (or adjectives
too, in other languages), as in:
"[quant,_1,document] were matched.\n"
Because if _1 is one, you get "1 document were matched".
An acceptable hack here is to do something like this:
"[quant,_1,document was, documents were] matched.\n"
$language->numf($number)
This returns the given number formatted nicely according
to this language's conventions. Maketext's default
method is mostly to just take the normal string form of
the number (applying sprintf "%G" for only very large
numbers), and then to add commas as necessary. (Except
that we apply "tr/,./.,/" if $language->{'numf_comma'}
is true; that's a bit of a hack that's useful for
languages that express two million as "2.000.000" and
not as "2,000,000").
If you want anything fancier, consider overriding this
with something that uses Number::Format, or does some-
thing else entirely.
Note that numf is called by quant for stringifying all
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quantifying numbers.
tems)@u-3p $language->sprintf($format, @items)
This is just a wrapper around Perl's normal "sprintf"
function. It's provided so that you can use "sprintf" in
Bracket Notation:
"Couldn't access datanode [sprintf,%10x=~[%s~],_1,_2]!\n"
returning...
Couldn't access datanode Stuff=[thangamabob]!
$language->language_tag()
Currently this just takes the last bit of
"ref($language)", turns underscores to dashes, and
returns it. So if $language is an object of class
Hee::HOO::Haw::en_us, $language->language_tag() returns
"en-us". (Yes, the usual representation for that
language tag is "en-US", but case is never considered
meaningful in language-tag comparison.)
You may override this as you like; Maketext doesn't use
it for anything.
$language->encoding()
Currently this isn't used for anything, but it's pro-
vided (with default value of "(ref($language) &&
$language->{'encoding'})) or "iso-8859-1"" ) as a sort
of suggestion that it may be useful/necessary to associ-
ate encodings with your language handles (whether on a
per-class or even per-handle basis.)
Language Handle Attributes and Internals
A language handle is a flyweight object -- i.e., it doesn't
(necessarily) carry any data of interest, other than just
being a member of whatever class it belongs to.
A language handle is implemented as a blessed hash. Subc-
lasses of yours can store whatever data you want in the
hash. Currently the only hash entry used by any crucial
Maketext method is "fail", so feel free to use anything else
as you like.
Remember: Don't be afraid to read the Maketext source if
there's any point on which this documentation is unclear.
This documentation is vastly longer than the module source
itself.
LANGUAGE CLASS HIERARCHIES
These are Locale::Maketext's assumptions about the class
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hierarchy formed by all your language classes:
+ You must have a project base class, which you load, and
which you then use as the first argument in the call to
YourProjClass->get_handle(...). It should derive
(whether directly or indirectly) from Locale::Maketext.
It doesn't matter how you name this class, altho assum-
ing this is the localization component of your Super
Mega Program, good names for your project class might be
SuperMegaProgram::Localization, SuperMegaProgram::L10N,
SuperMegaProgram::I18N, SuperMegaProgram::International,
or even SuperMegaProgram::Languages or
SuperMegaProgram::Messages.
+ Language classes are what YourProjClass->get_handle will
try to load. It will look for them by taking each
language-tag (skipping it if it doesn't look like a
language-tag or locale-tag!), turning it to all lower-
case, turning and dashes to underscores, and appending
it to YourProjClass . "::". So this:
$lh = YourProjClass->get_handle(
'en-US', 'fr', 'kon', 'i-klingon', 'i-klingon-romanized'
);
will try loading the classes YourProjClass::en_us (note
lowercase!), YourProjClass::fr, YourProjClass::kon,
YourProjClass::i_klingon and
YourProjClass::i_klingon_romanized. (And it'll stop at
the first one that actually loads.)
+ I assume that each language class derives (directly or
indirectly) from your project class, and also defines
its @ISA, its %Lexicon, or both. But I anticipate no
dire consequences if these assumptions do not hold.
+ Language classes may derive from other language classes
(altho they should have "use Thatclassname" or "use base
qw(...classes...)"). They may derive from the project
class. They may derive from some other class alto-
gether. Or via multiple inheritance, it may derive from
any mixture of these.
+ I foresee no problems with having multiple inheritance
in your hierarchy of language classes. (As usual, how-
ever, Perl will complain bitterly if you have a cycle in
the hierarchy: i.e., if any class is its own ancestor.)
ENTRIES IN EACH LEXICON
A typical %Lexicon entry is meant to signify a phrase, tak-
ing some number (0 or more) of parameters. An entry is
meant to be accessed by via a string key in
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$lh->maketext(key, ...parameters...), which should return a
string that is generally meant for be used for "output" to
the user -- regardless of whether this actually means print-
ing to STDOUT, writing to a file, or putting into a GUI
widget.
While the key must be a string value (since that's a basic
restriction that Perl places on hash keys), the value in the
lexicon can currently be of several types: a defined scalar,
scalarref, or coderef. The use of these is explained above,
in the section 'The "maketext" Method', and Bracket Notation
for strings is discussed in the next section.
While you can use arbitrary unique IDs for lexicon keys
(like "_min_larger_max_error"), it is often useful for if an
entry's key is itself a valid value, like this example error
message:
"Minimum ([_1]) is larger than maximum ([_2])!\n",
Compare this code that uses an arbitrary ID...
die $lh->maketext( "_min_larger_max_error", $min, $max )
if $min > $max;
...to this code that uses a key-as-value:
die $lh->maketext(
"Minimum ([_1]) is larger than maximum ([_2])!\n",
$min, $max
) if $min > $max;
The second is, in short, more readable. In particular, it's
obvious that the number of parameters you're feeding to that
phrase (two) is the number of parameters that it wants to be
fed. (Since you see _1 and a _2 being used in the key
there.)
Also, once a project is otherwise complete and you start to
localize it, you can scrape together all the various keys
you use, and pass it to a translator; and then the
translator's work will go faster if what he's presented is
this:
"Minimum ([_1]) is larger than maximum ([_2])!\n",
=> "", # fill in something here, Jacques!
rather than this more cryptic mess:
"_min_larger_max_error"
=> "", # fill in something here, Jacques
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I think that keys as lexicon values makes the completed lex-
icon entries more readable:
"Minimum ([_1]) is larger than maximum ([_2])!\n",
=> "Le minimum ([_1]) est plus grand que le maximum ([_2])!\n",
Also, having valid values as keys becomes very useful if you
set up an _AUTO lexicon. _AUTO lexicons are discussed in a
later section.
I almost always use keys that are themselves valid lexicon
values. One notable exception is when the value is quite
long. For example, to get the screenful of data that a
command-line program might returns when given an unknown
switch, I often just use a key "_USAGE_MESSAGE". At that
point I then go and immediately to define that lexicon entry
in the ProjectClass::L10N::en lexicon (since English is
always my "project language"):
'_USAGE_MESSAGE' => <<'EOSTUFF',
...long long message...
EOSTUFF
and then I can use it as:
getopt('oDI', \%opts) or die $lh->maketext('_USAGE_MESSAGE');
Incidentally, note that each class's %Lexicon inherits-and-
extends the lexicons in its superclasses. This is not
because these are special hashes per se, but because you
access them via the "maketext" method, which looks for
entries across all the %Lexicon's in a language class and
all its ancestor classes. (This is because the idea of
"class data" isn't directly implemented in Perl, but is
instead left to individual class-systems to implement as
they see fit..)
Note that you may have things stored in a lexicon besides
just phrases for output: for example, if your program takes
input from the keyboard, asking a "(Y/N)" question, you
probably need to know what equivalent of "Y[es]/N[o]" is in
whatever language. You probably also need to know what the
equivalents of the answers "y" and "n" are. You can store
that information in the lexicon (say, under the keys
"~answer_y" and "~answer_n", and the long forms as
"~answer_yes" and "~answer_no", where "~" is just an ad-hoc
character meant to indicate to programmers/translators that
these are not phrases for output).
Or instead of storing this in the language class's lexicon,
you can (and, in some cases, really should) represent the
same bit of knowledge as code is a method in the language
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class. (That leaves a tidy distinction between the lexicon
as the things we know how to say, and the rest of the things
in the lexicon class as things that we know how to do.)
Consider this example of a processor for responses to French
"oui/non" questions:
sub y_or_n {
return undef unless defined $_[1] and length $_[1];
my $answer = lc $_[1]; # smash case
return 1 if $answer eq 'o' or $answer eq 'oui';
return 0 if $answer eq 'n' or $answer eq 'non';
return undef;
}
...which you'd then call in a construct like this:
my $response;
until(defined $response) {
print $lh->maketext("Open the pod bay door (y/n)? ");
$response = $lh->y_or_n( get_input_from_keyboard_somehow() );
}
if($response) { $pod_bay_door->open() }
else { $pod_bay_door->leave_closed() }
Other data worth storing in a lexicon might be things like
filenames for language-targetted resources:
...
"_main_splash_png"
=> "/styles/en_us/main_splash.png",
"_main_splash_imagemap"
=> "/styles/en_us/main_splash.incl",
"_general_graphics_path"
=> "/styles/en_us/",
"_alert_sound"
=> "/styles/en_us/hey_there.wav",
"_forward_icon"
=> "left_arrow.png",
"_backward_icon"
=> "right_arrow.png",
# In some other languages, left equals
# BACKwards, and right is FOREwards.
...
You might want to do the same thing for expressing key bind-
ings or the like (since hardwiring "q" as the binding for
the function that quits a screen/menu/program is useful only
if your language happens to associate "q" with "quit"!)
BRACKET NOTATION
Bracket Notation is a crucial feature of Locale::Maketext.
I mean Bracket Notation to provide a replacement for sprintf
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formatting. Everything you do with Bracket Notation could be
done with a sub block, but bracket notation is meant to be
much more concise.
Bracket Notation is a like a miniature "template" system (in
the sense of Text::Template, not in the sense of C++ tem-
plates), where normal text is passed thru basically as is,
but text is special regions is specially interpreted. In
Bracket Notation, you use brackets ("[...]" -- not "{...}"!)
to note sections that are specially interpreted.
For example, here all the areas that are taken literally are
underlined with a "^", and all the in-bracket special
regions are underlined with an X:
"Minimum ([_1]) is larger than maximum ([_2])!\n",
^^^^^^^^^ XX ^^^^^^^^^^^^^^^^^^^^^^^^^^ XX ^^^^
When that string is compiled from bracket notation into a
real Perl sub, it's basically turned into:
sub {
my $lh = $_[0];
my @params = @_;
return join '',
"Minimum (",
...some code here...
") is larger than maximum (",
...some code here...
")!\n",
}
# to be called by $lh->maketext(KEY, params...)
In other words, text outside bracket groups is turned into
string literals. Text in brackets is rather more complex,
and currently follows these rules:
+ Bracket groups that are empty, or which consist only of
whitespace, are ignored. (Examples: "[]", "[ ]", or
a [ and a ] with returns and/or tabs and/or spaces
between them.
Otherwise, each group is taken to be a comma-separated
group of items, and each item is interpreted as follows:
+ An item that is "_digits" or "_-digits" is interpreted
as $_[value]. I.e., "_1" is becomes with $_[1], and
"_-3" is interpreted as $_[-3] (in which case @_ should
have at least three elements in it). Note that $_[0] is
the language handle, and is typically not named
directly.
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+ An item "_*" is interpreted to mean "all of @_ except
$_[0]". I.e., @_[1..$#_]. Note that this is an empty
list in the case of calls like $lh->maketext(key) where
there are no parameters (except $_[0], the language han-
dle).
+ Otherwise, each item is interpreted as a string literal.
The group as a whole is interpreted as follows:
+ If the first item in a bracket group looks like a method
name, then that group is interpreted like this:
$lh->that_method_name(
...rest of items in this group...
),
+ If the first item in a bracket group is "*", it's taken
as shorthand for the so commonly called "quant" method.
Similarly, if the first item in a bracket group is "#",
it's taken to be shorthand for "numf".
+ If the first item in a bracket group is empty-string, or
"_*" or "_digits" or "_-digits", then that group is
interpreted as just the interpolation of all its items:
join('',
...rest of items in this group...
),
Examples: "[_1]" and "[,_1]", which are synonymous; and
""[,ID-(,_4,-,_2,)]"", which compiles as "join "",
"ID-(", $_[4], "-", $_[2], ")"".
+ Otherwise this bracket group is invalid. For example,
in the group "[!@#,whatever]", the first item "!@#" is
neither empty-string, "_number", "_-number", "_*", nor a
valid method name; and so Locale::Maketext will throw an
exception of you try compiling an expression containing
this bracket group.
Note, incidentally, that items in each group are
comma-separated, not "/\s*,\s*/"-separated. That is, you
might expect that this bracket group:
"Hoohah [foo, _1 , bar ,baz]!"
would compile to this:
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sub {
my $lh = $_[0];
return join '',
"Hoohah ",
$lh->foo( $_[1], "bar", "baz"),
"!",
}
But it actually compiles as this:
sub {
my $lh = $_[0];
return join '',
"Hoohah ",
$lh->foo(" _1 ", " bar ", "baz"), #!!!
"!",
}
In the notation discussed so far, the characters "[" and "]"
are given special meaning, for opening and closing bracket
groups, and "," has a special meaning inside bracket groups,
where it separates items in the group. This begs the ques-
tion of how you'd express a literal "[" or "]" in a Bracket
Notation string, and how you'd express a literal comma
inside a bracket group. For this purpose I've adopted "~"
(tilde) as an escape character: "~[" means a literal '['
character anywhere in Bracket Notation (i.e., regardless of
whether you're in a bracket group or not), and ditto for
"~]" meaning a literal ']', and "~," meaning a literal
comma. (Altho "," means a literal comma outside of bracket
groups -- it's only inside bracket groups that commas are
special.)
And on the off chance you need a literal tilde in a bracket
expression, you get it with "~~".
Currently, an unescaped "~" before a character other than a
bracket or a comma is taken to mean just a "~" and that
character. I.e., "~X" means the same as "~~X" -- i.e., one
literal tilde, and then one literal "X". However, by using
"~X", you are assuming that no future version of Maketext
will use "~X" as a magic escape sequence. In practice this
is not a great problem, since first off you can just write
"~~X" and not worry about it; second off, I doubt I'll add
lots of new magic characters to bracket notation; and third
off, you aren't likely to want literal "~" characters in
your messages anyway, since it's not a character with wide
use in natural language text.
Brackets must be balanced -- every openbracket must have one
matching closebracket, and vice versa. So these are all
invalid:
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"I ate [quant,_1,rhubarb pie."
"I ate [quant,_1,rhubarb pie[."
"I ate quant,_1,rhubarb pie]."
"I ate quant,_1,rhubarb pie[."
Currently, bracket groups do not nest. That is, you cannot
say:
"Foo [bar,baz,[quux,quuux]]\n";
If you need a notation that's that powerful, use normal
Perl:
%Lexicon = (
...
"some_key" => sub {
my $lh = $_[0];
join '',
"Foo ",
$lh->bar('baz', $lh->quux('quuux')),
"\n",
},
...
);
Or write the "bar" method so you don't need to pass it the
output from calling quux.
I do not anticipate that you will need (or particularly
want) to nest bracket groups, but you are welcome to email
me with convincing (real-life) arguments to the contrary.
AUTO LEXICONS
If maketext goes to look in an individual %Lexicon for an
entry for key (where key does not start with an underscore),
and sees none, but does see an entry of "_AUTO" =>
some_true_value, then we actually define $Lexicon{key} = key
right then and there, and then use that value as if it had
been there all along. This happens before we even look in
any superclass %Lexicons!
(This is meant to be somewhat like the AUTOLOAD mechanism in
Perl's function call system -- or, looked at another way,
like the AutoLoader module.)
I can picture all sorts of circumstances where you just do
not want lookup to be able to fail (since failing normally
means that maketext throws a "die", altho see the next sec-
tion for greater control over that). But here's one cir-
cumstance where _AUTO lexicons are meant to be especially
useful:
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As you're writing an application, you decide as you go what
messages you need to emit. Normally you'd go to write this:
if(-e $filename) {
go_process_file($filename)
} else {
print "Couldn't find file \"$filename\"!\n";
}
but since you anticipate localizing this, you write:
use ThisProject::I18N;
my $lh = ThisProject::I18N->get_handle();
# For the moment, assume that things are set up so
# that we load class ThisProject::I18N::en
# and that that's the class that $lh belongs to.
...
if(-e $filename) {
go_process_file($filename)
} else {
print $lh->maketext(
"Couldn't find file \"[_1]\"!\n", $filename
);
}
Now, right after you've just written the above lines, you'd
normally have to go open the file ThisProject/I18N/en.pm,
and immediately add an entry:
"Couldn't find file \"[_1]\"!\n"
=> "Couldn't find file \"[_1]\"!\n",
But I consider that somewhat of a distraction from the work
of getting the main code working -- to say nothing of the
fact that I often have to play with the program a few times
before I can decide exactly what wording I want in the mes-
sages (which in this case would require me to go changing
three lines of code: the call to maketext with that key, and
then the two lines in ThisProject/I18N/en.pm).
However, if you set "_AUTO => 1" in the %Lexicon in,
ThisProject/I18N/en.pm (assuming that English (en) is the
language that all your programmers will be using for this
project's internal message keys), then you don't ever have
to go adding lines like this
"Couldn't find file \"[_1]\"!\n"
=> "Couldn't find file \"[_1]\"!\n",
to ThisProject/I18N/en.pm, because if _AUTO is true there,
then just looking for an entry with the key "Couldn't find
file \"[_1]\"!\n" in that lexicon will cause it to be added,
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with that value!
Note that the reason that keys that start with "_" are
immune to _AUTO isn't anything generally magical about the
underscore character -- I just wanted a way to have most
lexicon keys be autoable, except for possibly a few, and I
arbitrarily decided to use a leading underscore as a signal
to distinguish those few.
CONTROLLING LOOKUP FAILURE
If you call $lh->maketext(key, ...parameters...), and
there's no entry key in $lh's class's %Lexicon, nor in the
superclass %Lexicon hash, and if we can't auto-make key
(because either it starts with a "_", or because none of its
lexicons have "_AUTO => 1,"), then we have failed to find a
normal way to maketext key. What then happens in these
failure conditions, depends on the $lh object "fail" attri-
bute.
If the language handle has no "fail" attribute, maketext
will simply throw an exception (i.e., it calls "die", men-
tioning the key whose lookup failed, and naming the line
number where the calling $lh->maketext(key,...) was.
If the language handle has a "fail" attribute whose value is
a coderef, then $lh->maketext(key,...params...) gives up and
calls:
return &{$that_subref}($lh, $key, @params);
Otherwise, the "fail" attribute's value should be a string
denoting a method name, so that
$lh->maketext(key,...params...) can give up with:
return $lh->$that_method_name($phrase, @params);
The "fail" attribute can be accessed with the "fail_with"
method:
# Set to a coderef:
$lh->fail_with( \&failure_handler );
# Set to a method name:
$lh->fail_with( 'failure_method' );
# Set to nothing (i.e., so failure throws a plain exception)
$lh->fail_with( undef );
# Simply read:
$handler = $lh->fail_with();
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Now, as to what you may want to do with these handlers:
Maybe you'd want to log what key failed for what class, and
then die. Maybe you don't like "die" and instead you want
to send the error message to STDOUT (or wherever) and then
merely "exit()".
Or maybe you don't want to "die" at all! Maybe you could
use a handler like this:
# Make all lookups fall back onto an English value,
# but after we log it for later fingerpointing.
my $lh_backup = ThisProject->get_handle('en');
open(LEX_FAIL_LOG, ">>wherever/lex.log") || die "GNAARGH $!";
sub lex_fail {
my($failing_lh, $key, $params) = @_;
print LEX_FAIL_LOG scalar(localtime), "\t",
ref($failing_lh), "\t", $key, "\n";
return $lh_backup->maketext($key,@params);
}
Some users have expressed that they think this whole mechan-
ism of having a "fail" attribute at all, seems a rather
pointless complication. But I want Locale::Maketext to be
usable for software projects of any scale and type; and dif-
ferent software projects have different ideas of what the
right thing is to do in failure conditions. I could simply
say that failure always throws an exception, and that if you
want to be careful, you'll just have to wrap every call to
$lh->maketext in an eval { }. However, I want programmers
to reserve the right (via the "fail" attribute) to treat
lookup failure as something other than an exception of the
same level of severity as a config file being unreadable, or
some essential resource being inaccessible.
One possibly useful value for the "fail" attribute is the
method name "failure_handler_auto". This is a method
defined in class Locale::Maketext itself. You set it with:
$lh->fail_with('failure_handler_auto');
Then when you call $lh->maketext(key, ...parameters...) and
there's no key in any of those lexicons, maketext gives up
with
return $lh->failure_handler_auto($key, @params);
But failure_handler_auto, instead of dying or anything, com-
piles $key, caching it in $lh->{'failure_lex'}{$key} = $com-
plied, and then calls the compiled value, and returns that.
(I.e., if $key looks like bracket notation, $compiled is a
sub, and we return &{$compiled}(@params); but if $key is
just a plain string, we just return that.)
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The effect of using "failure_auto_handler" is like an AUTO
lexicon, except that it 1) compiles $key even if it starts
with "_", and 2) you have a record in the new hashref
$lh->{'failure_lex'} of all the keys that have failed for
this object. This should avoid your program dying -- as
long as your keys aren't actually invalid as bracket code,
and as long as they don't try calling methods that don't
exist.
"failure_auto_handler" may not be exactly what you want, but
I hope it at least shows you that maketext failure can be
mitigated in any number of very flexible ways. If you can
formalize exactly what you want, you should be able to
express that as a failure handler. You can even make it
default for every object of a given class, by setting it in
that class's init:
sub init {
my $lh = $_[0]; # a newborn handle
$lh->SUPER::init();
$lh->fail_with('my_clever_failure_handler');
return;
}
sub my_clever_failure_handler {
...you clever things here...
}
HOW TO USE MAKETEXT
Here is a brief checklist on how to use Maketext to localize
applications:
+ Decide what system you'll use for lexicon keys. If you
insist, you can use opaque IDs (if you're nostalgic for
"catgets"), but I have better suggestions in the section
"Entries in Each Lexicon", above. Assuming you opt for
meaningful keys that double as values (like "Minimum
([_1]) is larger than maximum ([_2])!\n"), you'll have
to settle on what language those should be in. For the
sake of argument, I'll call this English, specifically
American English, "en-US".
+ Create a class for your localization project. This is
the name of the class that you'll use in the idiom:
use Projname::L10N;
my $lh = Projname::L10N->get_handle(...) || die "Language?";
Assuming your call your class Projname::L10N, create a
class consisting minimally of:
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package Projname::L10N;
use base qw(Locale::Maketext);
...any methods you might want all your languages to share...
# And, assuming you want the base class to be an _AUTO lexicon,
# as is discussed a few sections up:
1;
+ Create a class for the language your internal keys are
in. Name the class after the language-tag for that
language, in lowercase, with dashes changed to under-
scores. Assuming your project's first language is US
English, you should call this Projname::L10N::en_us. It
should consist minimally of:
package Projname::L10N::en_us;
use base qw(Projname::L10N);
%Lexicon = (
'_AUTO' => 1,
);
1;
(For the rest of this section, I'll assume that this
"first language class" of Projname::L10N::en_us has
_AUTO lexicon.)
+ Go and write your program. Everywhere in your program
where you would say:
print "Foobar $thing stuff\n";
instead do it thru maketext, using no variable interpo-
lation in the key:
print $lh->maketext("Foobar [_1] stuff\n", $thing);
If you get tired of constantly saying "print
$lh->maketext", consider making a functional wrapper for
it, like so:
use Projname::L10N;
use vars qw($lh);
$lh = Projname::L10N->get_handle(...) || die "Language?";
sub pmt (@) { print( $lh->maketext(@_)) }
# "pmt" is short for "Print MakeText"
$Carp::Verbose = 1;
# so if maketext fails, we see made the call to pmt
Besides whole phrases meant for output, anything
language-dependent should be put into the class
Projname::L10N::en_us, whether as methods, or as lexicon
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entries -- this is discussed in the section "Entries in
Each Lexicon", above.
+ Once the program is otherwise done, and once its locali-
zation for the first language works right (via the data
and methods in Projname::L10N::en_us), you can get
together the data for translation. If your first
language lexicon isn't an _AUTO lexicon, then you
already have all the messages explicitly in the lexicon
(or else you'd be getting exceptions thrown when you
call $lh->maketext to get messages that aren't in
there). But if you were (advisedly) lazy and are using
an _AUTO lexicon, then you've got to make a list of all
the phrases that you've so far been letting _AUTO gen-
erate for you. There are very many ways to assemble
such a list. The most straightforward is to simply grep
the source for every occurrence of "maketext" (or calls
to wrappers around it, like the above "pmt" function),
and to log the following phrase.
+ You may at this point want to consider whether the your
base class (Projname::L10N) that all lexicons inherit
from (Projname::L10N::en, Projname::L10N::es, etc.)
should be an _AUTO lexicon. It may be true that in
theory, all needed messages will be in each language
class; but in the presumably unlikely or "impossible"
case of lookup failure, you should consider whether your
program should throw an exception, emit text in English
(or whatever your project's first language is), or some
more complex solution as described in the section "Con-
trolling Lookup Failure", above.
+ Submit all messages/phrases/etc. to translators.
(You may, in fact, want to start with localizing to one
other language at first, if you're not sure that you've
property abstracted the language-dependent parts of your
code.)
Translators may request clarification of the situation
in which a particular phrase is found. For example, in
English we are entirely happy saying "n files found",
regardless of whether we mean "I looked for files, and
found n of them" or the rather distinct situation of "I
looked for something else (like lines in files), and
along the way I saw n files." This may involve rethink-
ing things that you thought quite clear: should "Edit"
on a toolbar be a noun ("editing") or a verb ("to
edit")? Is there already a conventionalized way to
express that menu option, separate from the target
language's normal word for "to edit"?
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In all cases where the very common phenomenon of quan-
tification (saying "N files", for any value of N) is
involved, each translator should make clear what depen-
dencies the number causes in the sentence. In many
cases, dependency is limited to words adjacent to the
number, in places where you might expect them ("I found
the-?PLURAL N empty-?PLURAL directory-?PLURAL"), but in
some cases there are unexpected dependencies ("I
found-?PLURAL ..."!) as well as long-distance dependen-
cies "The N directory-?PLURAL could not be
deleted-?PLURAL"!).
Remind the translators to consider the case where N is
0: "0 files found" isn't exactly natural-sounding in any
language, but it may be unacceptable in many -- or it
may condition special kinds of agreement (similar to
English "I didN'T find ANY files").
Remember to ask your translators about numeral format-
ting in their language, so that you can override the
"numf" method as appropriate. Typical variables in
number formatting are: what to use as a decimal point
(comma? period?); what to use as a thousands separator
(space? nonbreaking space? comma? period? small middot?
prime? apostrophe?); and even whether the so-called
"thousands separator" is actually for every third digit
-- I've heard reports of two hundred thousand being
expressible as "2,00,000" for some Indian (Subcontinen-
tal) languages, besides the less surprising "200 000",
"200.000", "200,000", and "200'000". Also, using a set
of numeral glyphs other than the usual ASCII "0"-"9"
might be appreciated, as via "tr/0-9/\x{0966}-\x{096F}/"
for getting digits in Devanagari script (for Hindi, Kon-
kani, others).
The basic "quant" method that Locale::Maketext provides
should be good for many languages. For some languages,
it might be useful to modify it (or its constituent
"numerate" method) to take a plural form in the two-
argument call to "quant" (as in "[quant,_1,files]") if
it's all-around easier to infer the singular form from
the plural, than to infer the plural form from the
singular.
But for other languages (as is discussed at length in
Locale::Maketext::TPJ13), simple "quant"/"numerify" is
not enough. For the particularly problematic Slavic
languages, what you may need is a method which you pro-
vide with the number, the citation form of the noun to
quantify, and the case and gender that the sentence's
syntax projects onto that noun slot. The method would
then be responsible for determining what grammatical
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number that numeral projects onto its noun phrase, and
what case and gender it may override the normal case and
gender with; and then it would look up the noun in a
lexicon providing all needed inflected forms.
+ You may also wish to discuss with the translators the
question of how to relate different subforms of the same
language tag, considering how this reacts with
"get_handle"'s treatment of these. For example, if a
user accepts interfaces in "en, fr", and you have inter-
faces available in "en-US" and "fr", what should they
get? You may wish to resolve this by establishing that
"en" and "en-US" are effectively synonymous, by having
one class zero-derive from the other.
For some languages this issue may never come up (Danish
is rarely expressed as "da-DK", but instead is just
"da"). And for other languages, the whole concept of a
"generic" form may verge on being uselessly vague, par-
ticularly for interfaces involving voice media in forms
of Arabic or Chinese.
+ Once you've localized your program/site/etc. for all
desired languages, be sure to show the result (whether
live, or via screenshots) to the translators. Once they
approve, make every effort to have it then checked by at
least one other speaker of that language. This holds
true even when (or especially when) the translation is
done by one of your own programmers. Some kinds of sys-
tems may be harder to find testers for than others,
depending on the amount of domain-specific jargon and
concepts involved -- it's easier to find people who can
tell you whether they approve of your translation for
"delete this message" in an email-via-Web interface,
than to find people who can give you an informed opinion
on your translation for "attribute value" in an XML
query tool's interface.
SEE ALSO
I recommend reading all of these:
Locale::Maketext::TPJ13 -- my The Perl Journal article about
Maketext. It explains many important concepts underlying
Locale::Maketext's design, and some insight into why Mak-
etext is better than the plain old approach of just having
message catalogs that are just databases of sprintf formats.
File::Findgrep is a sample application/module that uses
Locale::Maketext to localize its messages. For a larger
internationalized system, see also Apache::MP3.
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I18N::LangTags.
Win32::Locale.
RFC 3066, Tags for the Identification of Languages, as at
http://sunsite.dk/RFC/rfc/rfc3066.html
RFC 2277, IETF Policy on Character Sets and Languages is at
http://sunsite.dk/RFC/rfc/rfc2277.html -- much of it is just
things of interest to protocol designers, but it explains
some basic concepts, like the distinction between locales
and language-tags.
The manual for GNU "gettext". The gettext dist is available
in "ftp://prep.ai.mit.edu/pub/gnu/" -- get a recent gettext
tarball and look in its "doc/" directory, there's an easily
browsable HTML version in there. The gettext documentation
asks lots of questions worth thinking about, even if some of
their answers are sometimes wonky, particularly where they
start talking about pluralization.
The Locale/Maketext.pm source. Obverse that the module is
much shorter than its documentation!
COPYRIGHT AND DISCLAIMER
Copyright (c) 1999-2004 Sean M. Burke. All rights reserved.
This library is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.
This program is distributed in the hope that it will be use-
ful, but without any warranty; without even the implied war-
ranty of merchantability or fitness for a particular pur-
pose.
AUTHOR
Sean M. Burke "sburke@cpan.org"
perl v5.8.8 2005-02-05 25
