Slides from my talk on Domain Specific Languages at PF-Congress, 2010. Original synopsis: While external Domain Specific Languages has always been a natural part of PHP development, the recent awareness of the internal DSL style of programming has been relatively slow to enter the PHP world. In this talk I'll give a short introduction to DSL's and the difference between the external and internal style. I'll then focus on the internal DSL style and show some common techniques and patterns used in the PHP world, giving examples as we move along.

1. Domain Specific Languages

2. I am Troels Knak-Nielsen. From Copenhagen. Have worked with web and PHP for about a decade.

3. Concepts Examples Perspective Questions

4. <?php class PurchaseHandler { protected $customer; function __construct(Customer $customer) { $this->customer = $customer; } function register(EventDispatcher $event_dispatcher) { $event_dispatcher->registerOnPurchase( PurchaseType::CAR, $customer, array($this, 'onPurchase')); } function onPurchase(Car $car) { $account = $this->customer->getAccount(); $account->withdraw($car->getPrice()); } } General Purpose Language (PHP)

5. when customer purchase (car) withdraw (priceof car) from (customer account) Domain Specific Language

7. Styles

8. Language Pipeline Grammar Parser Internal Representation Runtime Environment

9. &quot;&quot;Some people, when confronted with a problem, think &quot;I know, I'll use regular expressions.&quot; Now they have two problems.&quot;&quot; -- Jamie Zawinski

10. when customer purchase (car) withdraw (priceof car) from (customer account) External style

11. when(customer(purchase(CAR)), withdraw(priceof(CAR))->from(customer(ACCOUNT))); Internal style

12. Concepts Examples Perspective Questions

13. Method Chaining

14. $select = $db->select() ->from('products') ->where('price > 4'); Zend_Db_Select

15. $bowling = new Bowling; describe($bowling)-> score->should()->be(0)-> when('When bowling has not yet started'); describe($bowling)-> score->shouldNot()->beGreaterThan(0)-> when('When bowling has not yet started'); PhpSpec

16. Global Symbols

17. when(customer(purchase(CAR)), withdraw(priceof(CAR))->from(customer(ACCOUNT))); The car-salesman

18. Lambda/ Scope

19. with('request')->begin(function($request) { $request->isParameter('module', 'foo'); $request->isParameter('action', 'index'); });

20. $browser-> get('/')-> with('request')->begin()-> isParameter('module', 'foo')-> isParameter('action', 'index')-> end()-> checkResponseElement('h1', 'foo') ; Symfony sfBrowser

21. Monadic Style

22. $customer_ids = array('22731', '2458', '14442'); snapshot( 'bg_account_detail', 'bg_adjustment', where('account_id', select('account_id', 'bg_account', where('customer_id', $customer_ids)))); .......................................................................... function select($column, $table, $condition = null) { return new Selection($column, $table, $condition); } function where($column, $value) { return new Condition($column, $value); }

23. Macros

24. stream_wrapper_register Allows you to implement your own protocol handlers and streams for use with all the other filesystem functions (such as fopen(), fread() etc.).

25. Hybrid External/ Internal

26. pq($li)->addClass('my-second-new-class'); .......................................................................... $q = Doctrine_Query::create() ->select('u.id') ->from('User u'); phpQuery Doctrine

27. Concepts Examples Perspective Questions

28. Why Bother?

29. Language Design

30. &quot;&quot;With great power comes great responsibility.&quot;&quot; -- Uncle Ben

31. Questions?

32. Follow me on @troelskn