locale.scala

scala> import rapture.i18n._
import rapture.i18n._

scala> import languages._
import languages._

// This would typically be a runtime value, but we'll just use "FR" as a fixed example
scala> val localeString = "FR"
localeString: String = FR

// Note that our Locale implicit is typed on the possible languages
scala> implicit val locale = (en | fr | la).parse(localeString)
locale: rapture.i18n.Locale[rapture.i18n.En with rapture.i18n.Fr with rapture.i18n.La] = fr

// That was the single point in the program that a runtime error could occur. From now on, we're safe!

// We have provided a message in a superset of these languages
scala> val msg = en"Hello" | fr"Bonjour" | de"Hallo" | la"Salve"
msg: rapture.i18n.I18n[String,rapture.i18n.En with rapture.i18n.Fr with rapture.i18n.De with rapture.i18n.La] = en|fr|de|la:Hello

// This will automatically convert to a String, using the implicit Locale
scala> msg: String
res0: String = Bonjour

// But if we do not provide all the languages, like this...
scala> val msg2 = fr"Au revoir" | it"Ciao"
msg2: rapture.i18n.I18n[String,rapture.i18n.Fr with rapture.i18n.It] = fr|it:Au revoir

// ...then we get a type error
scala> msg2: String
<console>:19: error: type mismatch;
 found   : rapture.i18n.I18n[String,rapture.i18n.Fr with rapture.i18n.It]
 required: String
              msg2: String
              ^
// This doesn't work because we would not be not be able to handle the cases where localeString was "EN" or "DE".