View source for Internationalization of Haskell programs

== Approaches to internationalization in Haskell ==

There are several different approaches you can use to internationalize
your Haskell program.

=== Using GNU gettext ===

You can internationalize your program using
[http://www.gnu.org/software/gettext/ GNU gettext]
and its Haskell bindings package
[http://hackage.haskell.org/package/hgettext hgettext].

Set up your translations and integrate them into your
application using
[[Internationalization of Haskell programs using gettext|these instructions]].

=== Using native Haskell data types ===

The [[Web/Frameworks#Yesod|Yesod web framework]] [http://www.yesodweb.com/book/internationalization takes this approach but provides a more translator-friendly format].

You can internationalize your program using native Haskell data types.

Represent the individual
texts to be translated as constructors of a Haskell data
type. Then provide a function that automatically renders
the texts appropriately in the current language context.

See
[[Internationalization of Haskell programs using Haskell data types|this description]]
of a simple example of using Haskell data types
for internationalization.

=== Using the Grammatical Framework ===

You can internationalize your program using the
[http://www.grammaticalframework.org/ Grammatical Framework] (GF).

The GF provides a way to define human-language-independent syntax
for expressing texts in Haskell.
The GF can then render the texts automatically
in any human language for which
an appropriate GF grammer exists.

See this
[https://github.com/creswick/gfI8N very simple example]
of an application internationalized using GF.
It is based on the "Foods" grammar (included in the example),
so it's quite contrived,
but it should be enough to get you started.
Usage instructions are in the file <code>README.md</code>.

See the
[http://www.grammaticalframework.org/download/index.html GF download page]
for information about how to install GF.
The standard installation of GF currently includes grammars
for at least 26 languages.

== Comparison of approaches to internationalization ==

=== GNU gettext ===

Advantages:

* Easiest integration with other tools and programming languages
* Little or no specialized knowledge required of translators
* Little or no interaction needed between programmers and translators
* Well-known and well-documented

Disadvantages:

* Inflexible use of static text literals creates awkwardness when there are complex differences between how the same idea is expressed in different languages
* Translation selection happens at runtime, so there is no type safety
* Texts are loaded from external files at runtime, which creates overhead and deployment issues
* Requires a moderate amount of work to set up and integrate
* Not well supported on MS Windows

=== Native Haskell data types ===

Advantages:

* Easy to implement in Haskell
* Compile-time type safety
* Fast
* Flexible in handling complex differences between languages
* Flexible in implementation: e.g., use a type class if you don't want one big data type, use Text or Builder instead of String
* Platform independent

Disadvantages:

* May require some training of translators and/or cooperative integration work between translators and programmers, depending on the level of sophistication needed in the rendering functions
* May lead to many string literals in a Haskell source file. This requires a work-around for a current limitation of the GHC compiler; see [[#file-embed|file-embed]], below.

=== Yesod's Native Data type approach ===

Yesod's approach provides a translator-friendly veneer that gets rid of the above disadvantages. It is integrated with the Yesod web framework and its use of the Hamlet template language.

A portion of it has been abstracted out into the 
http://hackage.haskell.org/package/shakespeare-i18n package.

=== Grammatical Framework ===

Advantages:

* Translations automatically generated in all languages for which GF grammars exist, without the need for human translators
* High quality translations
* Platform independent

Disadvantages:

* Learning curve for the programmer to express texts using existing GF grammars, and to extend GF grammars as needed
* Extra work needed if you must support languages that do not yet have a GF grammar
* Installing GF is not quite as simple as installing the usual Haskell package
* A human translator may still be needed for domain-specific words and expressions not included in the standard GF grammars

== Other tools ==

The following tools may also be useful when internationalizing your Haskell program:

=== file-embed ===

Internationalization often leads to a large number of literal
strings in a Haskell source file. This creates a technical
problem due to a current limitation of the GHC compiler -
the GHC compiler does not behave well when compiling a source
file with a large number of literal strings.

One classic work-around to this problem is to place the literal
strings in a small C library and import them via the FFI.

Another work-around, based on Template Haskell, is provided by
the
[http://hackage.haskell.org/package/file-embed file-embed]
package.

=== numerals ===

The
[http://hackage.haskell.org/package/numerals numerals]
package renders numbers
(currently only cardinal numbers)
as text in many different languages.