Ajaxian.com published an article on Ojay, an interesting JavaScript library that rests on top of Yahoo!’s YUI. The library has a DSLish way of expressing form validation rules, like in these snippets from their website:

form('signup')
  .requires('username').toHaveLength({minimum: 6})
  .requires('email').toMatch(EMAIL_FORMAT, 'must be a valid email address')
  .expects('email_conf').toConfirm('email')
  .expects('title').toBeOneOf(['Mr', 'Mrs', 'Miss'])
  .requires('dob', 'Birth date').toMatch(/^\d{4}\D*\d{2}\D*\d{2}$/)
  .requires('tickets').toHaveValue({maximum: 12})
  .requires('phone')
  .requires('accept', 'Terms and conditions').toBeChecked('must be accepted');
//...
    form('signup').submitsUsingAjax();
    when('signup').responseArrives(displayResponseIn(result));
}});

What makes this a Domain-Specific Language? The code written above is clearly something different from the standard high-order-programming-like JavaScript style. The author of the library changed the language so it could represent the domain in a more expressive way. An Internal DSL is a language adaptation focusing on writing expressive or more efficient code for a given domain.

Browsing the documentation I found how keyboard events are defined in Ojay:

var rulesA = new Ojay.Keyboard.RuleSet({
              'SHIFT S':    function() { alert('S') },
              'CONTROL Y':  function() { alert('Y') }
            });
            rulesA.enable();

Recently I’ve been playing around keyboard event definition in a toy Domain-Specific Language so this caught my attention. I really don’t like Strings used as commands, the DSL I’m writing uses a fancier syntax for keyboard event handlers the focusing in removing some syntactic noise.

Here is the equivalent code using my Ruby Hotkeys DSL:

rules_a = @dsl.map {{
[shift] + [s] => lambda{ puts 'S'},
[crtl] + [y] => lambda{ puts 'Y'}
}}

The Hotkey DSL won’t be production-ready, it’s just a proof-of-concept of some ideas I have. Anyway I can imagine that getting something like this is JavaScript won’t be that hard. Actually, I reckon it is very easy to have something like this:

var rulesA = new Ojay.Keyboard.RuleSet([
              hotkey([shift] + [S], function() { alert('S') }),
              hotkey([ctrl] + [y], function() { alert('Y') })
            ]);
            rulesA.enable();

It is still verbose but at least we have something less noisy and more expressive than strings.