9.1. Growing language support for DSL design

DSLs are all about being expressive with respect to the domain that you model. When you’re modeling an accounting system, you want your API set to speak in terms of debits, credits, books, ledgers, and journals. But these are only the nouns of the model, the concrete artifacts that form some of the core concepts in the problem domain. You also need to convey the verbs with the same level of expressiveness that you speak in the problem space. Remember our coffee shop example in chapter 1 that started us off? The barista could serve precisely what you ordered because you spoke in the language she understands. The whole expression needs to have a synergy with the problem domain that’s being modeled. Consider the following snippet of Scala code that we discussed in chapter 3:

withAccount(trade) {
  account => {
    settle(
      trade using
        account.getClient
               .getStandingRules
               .filter(_.account == account)
               .first)
    andThen journalize
  }
}