[web-devel] [Yesod] rendering different templates for different languages

[Michael Snoyman]

Let's look at a more concrete example: you have an online store
selling male dogs and female cats. So you would have:

    data Basket = Basket { maleDogs :: Int, femaleCats :: Int }

What you need is a function such as:

    renderBasket :: Basket -> String

for each language. In English, this could be something like:

    pluralize :: Int -> (String, String) -> String
    pluralize 1 (x, _) = x
    pluralize _ (_, x) = x

    renderBasket (Basket dogs cats) = concat
        [ "You have decided to purchase "
        , show dogs
        , pluralize dogs ("dog", "dogs")
        , " and "
        , show cats
        , pluralize cats ("cat", "cats")
        ]

In Hebrew, some words (like years) have a singular, plural *and* dual
form, so pluralize for Hebrew may look like:

    pluralize :: Int -> (String, Maybe String, String) -> String
    pluralize 1 (x, _, _) = x ++ " אחד" -- in Hebrew, the "one" comes
after the word, all other numbers before
    pluralize 2 (_, Just x, _) = x -- for dual form, you never show
the number, it is assumed
    pluralize i (_, _, x) = show i ++ " " ++ x -- for the plural, put
the number before

If we could build up a library in Haskell of such helper functions, I
think it would make translating applications much simpler. But this is
the point where we would need a lot of collaboration: I can help out
on English and Hebrew (and if I still remember it, Spanish), but I
don't know a thing about Japanese, Russian, or most other languages in
the world.

I'm not sure how much it would really help to use typeclasses here,
however. I think for the most part it will just be an issue of having
a separate module for each language. What I'd *really* like to figure
out is how to make a nice, easy-to-use wrapper around all of this for
translators, who will likely not know any Haskell. Perhaps a language
similar to Hamlet:

    # strings-english.trans
    Hello: Hello
    Person name age: #{name} is #{age} #{pluralize age "year" "years"} old.
    Basket dogs cats: You have purchased #{dogs} #{pluralize dogs
"dog" "dogs"} and #{cats} #{pluralize cats "cat" cats"}.

Michael

On Mon, Feb 21, 2011 at 8:57 AM, Ian Duncan <iand675 at gmail.com> wrote:
> And of course in some languages such as Japanese, there are barely any
> gender distinctions or such things as pluralization at all. Perhaps we need
> pluralization, conjugation, and 'genderization' typeclasses with instances
> defined for different language datatypes?
>
> --
> Ian Duncan
>
> On Monday, February 21, 2011 at 12:46 AM, Michael Snoyman wrote:
>
> The other day I was speaking with a woman on the train. She was
> telling me about her daughters. I wanted to ask her how old they are,
> but I got the pluralization wrong and instead of saying "bnot kama"
> (plural) I said "bat kama," (singular) to which she responded 36.
>
> tl;dr: You can offend people just was well with pluralization issues
> as with gender issues.
>
> Michael
>
> On Mon, Feb 21, 2011 at 8:40 AM, Max Cantor <mxcantor at gmail.com> wrote:
>
> Of course, you just pointed out one of the big difficulties with i18n.  I
> dont think you're wife would take kindly to you referring to her in the male
> gender.  so now, you need the person's gender too.  i18n is hard :(  the
> whole would should switch to esperanto.
>
> max
>
> On Feb 21, 2011, at 2:25 PM, Michael Snoyman wrote:
>
> A proper i18n solution is high on my wish list right now, but I've
> purposely avoided implementing one so far since I'd rather wait until
> I think we have a good solution as opposed to implementing an
> acceptable solution now. But let me share my ideas, it might help you
> out here.
>
> In general, it's very uncommon that you need a completely separate set
> of templates for each language. Your markup, classes, styles, and
> logic will likely be identical for each language, and creating a
> separate template for each will just result in a lot of pain in the
> long run. Instead, you're likely better off having a single template
> and just translating strings.
>
> I've blogged about this before[1]. My idea is to use a datatype for
> your translatable strings, and then have a function that takes a
> language and a value and returns the translated string. A simple
> example:
>
>    data Strings = Hello | Person String Int
>    toEnglish Hello = "Hello"
>    toEnglish (Person name age) = name ++ " is " ++ show age ++ "
> years old" -- obviously need to check if person is 1 year old and
> correct
>
>    toHebrew Hello = "שלום"
>    toHebrew (Person name age) = name ++ " הוא בן " ++ show age ++ " שנים"
>
> The nice thing about this approach is you have the full power of
> Haskell to address typical translation issues, such as pluralization,
> word order and gender matching. (As a counter example, at work, we use
> XSLT for this, and then you get the full power of XSLT for solving the
> problem ::cringe::.)
>
> You can then use the languages[2] function from Yesod to help you out:
>
>    getRenderString = chooseFunc `fmap` languages
>       where
>         chooseFunc [] = toEnglish -- default language
>         chooseFunc ("en":_) = toEnglish
>         chooseFunc ("he":_) = toHebrew
>         chooseFunc (_:x) = chooseFunc x
>
> Then you can write a handler function like:
>
> getPersonR name age = do
>    render <- getRenderString
>    defaultLayout [$hamlet|
> <h1>#{render Hello}
> <p>#{render $ Person name age}
> |]
>
> Which will work for English and Hebrew just fine. Ideally, I would
> like to add support to Hamlet for this directly, involving a String
> rendering function similar to the URL rendering function already in
> place. But for the moment, this should work.
>
> I'd love to hear peoples opinions about this.
>
> Michael
>
> [1] http://docs.yesodweb.com/blog/i18n-in-haskell
> [2]
> http://hackage.haskell.org/packages/archive/yesod-core/0.7.0.1/doc/html/Yesod-Request.html#v:languages
>
> On Sun, Feb 20, 2011 at 11:19 PM, Dmitry Kurochkin
> <dmitry.kurochkin at gmail.com> wrote:
>
> Hi all.
>
> I want a handler to render different templates for different languages.
> I have getCurrentLanguage function and now I try to do something like:
>
>    getRootR = do
>        currentLanguage <- getCurrentLanguage
>        defaultLayout $ do
>            addWidget $(widgetFile $ currentLanguage ++ "/homepage")
>
> This results in:
>
>    GHC stage restriction: `currentLanguage'
>      is used in a top-level splice or annotation,
>      and must be imported, not defined locally
>
> This makes sense to me, because TH is calculated at compile time. I
> would like to hear ideas how to work around this restriction. Perhaps
> there is an existing solution in Yesod?
>
> At the moment, the best I could think of is smth like this:
>
>    getRootR = do
>        currentLanguage <- getCurrentLanguage
>        defaultLayout $ do
>            case currentLanguage of
>                "en" -> addWidget $(widgetFile  "en/homepage")
>                ... and so on for each language ...
>
> Obviously, this is not a solution taking in account that there are many
> languages and many handlers.
>
> I was considering creating a global (template file name -> rendered
> template) map. But I am not sure this is really feasible.
>
> Regards,
>  Dmitry
>
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