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Domain Specific Languages

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

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Concepts Examples Perspective Questions

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<?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)

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

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Styles

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Language Pipeline Grammar Parser Internal Representation Runtime Environment

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&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

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

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

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Concepts Examples Perspective Questions

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Method Chaining

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

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$bowling = new Bowling; describe($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

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Global Symbols

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

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Lambda/ Scope

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

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

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Monadic Style

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$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); }

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Macros

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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.).

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Hybrid External/ Internal

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

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Concepts Examples Perspective Questions

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Why Bother?

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Language Design

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

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Questions?

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Follow me on @troelskn