Language-Oriented Programming and Language Workbenches: Building Domain Languages Atop Java Technology

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1. ThoughtWorks Language-Oriented Programming and Language Workbenches: Building Domain Languages Atop Java™ Technology Neal Ford ThoughtWorker/Meme Wrangler…
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  • 1. ThoughtWorks Language-Oriented Programming and Language Workbenches: Building Domain Languages Atop Java™ Technology Neal Ford ThoughtWorker/Meme Wrangler ThoughtWorks www.thoughtworks.com Session TS-1589 2007 JavaOneSM Conference | Session TS-1589 |
  • 2. What This Session Covers • Motivation • Internal vs. external DSLs • Building internal DSLs in • Java technology • Groovy • Ruby (via JRuby) • Building external DSLs • DSL best practices 2007 JavaOneSM Conference | Session TS-1589 | 2
  • 3. Questions • Why is there so much XML mixed in with my Java code? • Why do we need things like aspects? • Why won’t everyone shut up already about Ruby on Rails? • Is there an evolutionary step beyond object- oriented programming? 2007 JavaOneSM Conference | Session TS-1589 | 3
  • 4. Modeling the World With Trees 2007 JavaOneSM Conference | Session TS-1589 | 4
  • 5. Modeling the Real World 2007 JavaOneSM Conference | Session TS-1589 | 5
  • 6. Changing Abstraction Styles • Layers of abstraction using language • Not trees • Trees and hierarchies still exist • Underneath a stronger abstraction layer • Objects, aspects, generics, et al become the building blocks for DSLs • Allows developers to work at a higher level of abstraction • Declarative vs. imperative programming 2007 JavaOneSM Conference | Session TS-1589 | 6
  • 7. Why Use DSLs for Abstraction? • “Iced decaf triple grande vanilla skim with whip latte” • “Scattered, smothered, covered” • The Waffle House Hash Brown language has 8 keywords (all inflected verbs) • Scattered, smothered, covered, chunked, topped, diced, peppered, and capped • “Route 66, swinging, easy on the chorus, extra solo at the coda, and bump at the end” • “OMFG D00d Bob is t3h UBER 1337 R0XX0RZ LOL” 2007 JavaOneSM Conference | Session TS-1589 | 7
  • 8. Including Your Business • Even if you are a Java technology ace • You still have to learn the DSL for your business on day 1 • This is the hardest part of your job 2007 JavaOneSM Conference | Session TS-1589 | 8
  • 9. Observation Every non-trivial human behavior has a domain specific language. 2007 JavaOneSM Conference | Session TS-1589 | 9
  • 10. Nomenclature • Coined by Martin Fowler • Domain-specific language • A limited form of computer language designed for a specific class of problems • Language-oriented programming • The general style of development which operates about the idea of building software around a set of domain specific languages 2007 JavaOneSM Conference | Session TS-1589 | 10
  • 11. DSLs vs. APIs • An API has an explicit context Coffee latte = new Coffee(Size.VENTI); latte.setFatContent(FatContent.NON_FAT); latte.setWhip(Whip.NONE); latte.setFoam(Foam.NONE); latte.setTemperature(Temp.EXTRA_HOT); latte.setStrength(5); 2007 JavaOneSM Conference | Session TS-1589 | 11
  • 12. DSLs vs. APIs • DSLs have an implicit context • Consider the real-world examples • The context is never mentioned • Once a context is established, repeating it over and over is just noise Venti half-caf, non-fat, extra hot, no foam, no whip latte 2007 JavaOneSM Conference | Session TS-1589 | 12
  • 13. Internal vs. External DSLs • Internal DSLs sit atop your base language • Must follow the syntax rules of the base language • Why Groovy and Ruby make better bases • External DSLs • Create a lexer and parser • Can take on any syntax you like • Let your imagination be your guide! • Hard to create… 2007 JavaOneSM Conference | Session TS-1589 | 13
  • 14. Fluent Interface • Creating a readable model • Convert APIs to English-like sentences • Slightly harder to write • Much easier to read 2007 JavaOneSM Conference | Session TS-1589 | 14
  • 15. Car API Car car = new CarImpl(); MarketingDescription desc = new MarketingDescriptionImpl(); desc.setType(quot;Boxquot;); desc.setSubType(quot;Insulatedquot;); desc.setAttribute(quot;lengthquot;, quot;50.5quot;); desc.setAttribute(quot;ladderquot;, quot;yesquot;); desc.setAttribute(quot;lining typequot;, quot;corkquot;); car.setDescription(desc); 2007 JavaOneSM Conference | Session TS-1589 | 15
  • 16. Car Fluent Interface Car car = new CarImpl().withMarketingDescriptionOf( new MarketingDescriptionImpl(quot;Boxquot;, quot;Insulated”). andAttributeOf(quot;lengthquot;, quot;50.5quot;). andIncludesA(quot;ladderquot;). andAttributeOf(quot;lining typequot;, quot;corkquot;)); 2007 JavaOneSM Conference | Session TS-1589 | 16
  • 17. Existing Fluent Interfaces 2007 JavaOneSM Conference | Session TS-1589 | 17
  • 18. Fluent Interface: Hamcrest • Hamcrest is an open source library from Google that creates fluent interfaces around JUnit matchers assertThat(theBiscuit, equalTo(myBiscuit)); assertThat(theBiscuit, is(equalTo(myBiscuit))); assertThat(theBiscuit, is(myBiscuit)); 2007 JavaOneSM Conference | Session TS-1589 | 18
  • 19. Fluent Interface: Mocks • JMock class PublisherTest extends MockObjectTestCase { public void testOneSubscriberReceivesAMessage() { Mock mockSubscriber = mock(Subscriber.class); Publisher publisher = new Publisher(); publisher.add((Subscriber) mockSubscriber.proxy()); final String message = quot;messagequot;; // expectations mockSubscriber.expects(once()). method(quot;receivequot;).with(eq(message)); // execute publisher.publish(message); } } 2007 JavaOneSM Conference | Session TS-1589 | 19
  • 20. Building Internal DSLs In Java Technology 2007 JavaOneSM Conference | Session TS-1589 | 20
  • 21. Example: Logging Configuration • Logger setup is ugly • Very API-ish • Uses • A properties file • Code • An XML file • Demo • LoggingConfiguration.java 2007 JavaOneSM Conference | Session TS-1589 | 21
  • 22. Fluent Interface: Wrapping iBatis • Humane interfaces improve the readability of any code • You can wrap existing APIs in fluent interfaces • Example • iBatis is an open source O/R mapping tool • It drips of API style of coding • Wrapping iBatis access in a fluent interface • Demo • EventPersisterImpl.java 2007 JavaOneSM Conference | Session TS-1589 | 22
  • 23. Java Technology: A Calendar DSL • Goal • Create a calendar application in Java technology using DSL techniques • Primarily uses fluent interface • Demo • Appointment.java • AppointmentCalendar.java • CalendarDemo.java 2007 JavaOneSM Conference | Session TS-1589 | 23
  • 24. Building Internal DSLs In Groovy 2007 JavaOneSM Conference | Session TS-1589 | 24
  • 25. Internal DSLs in Groovy • Groovy makes a better base for DSLs • Open classes via categories • Closures • Looser syntax rules • Dynamic typing 2007 JavaOneSM Conference | Session TS-1589 | 25
  • 26. Building Blocks: Closures • Closures mimic scope capturing method pointers • Like a method, a closure defines a scope • Can still reference variables from the enclosing scope • Accepts parameters • Allows “with” semantics with categories • In a DSL, provides containership semantics 2007 JavaOneSM Conference | Session TS-1589 | 26
  • 27. Building Blocks: Open Classes • Open Classes via categories • Groovy allows you to attach methods to an existing class • Either Groovy or Java Development Kit (JDK™) • Yes, you can add methods to String • Categories are classes with static methods • Each method’s first parameter is self • Fake object-orientation • Category demo = Adding methods to String 2007 JavaOneSM Conference | Session TS-1589 | 27
  • 28. Time DSL in Groovy • The goal: create a fluent interface around time spans and calendars • Target syntax 2.days.fromToday.at(4.pm) • Returns a calendar for that date and time • Demo • IntegerWithTimeSupport.groovy • CalendarDsl.groovy • TestTime.groovy • CalendarDslDemo.groovy 2007 JavaOneSM Conference | Session TS-1589 | 28
  • 29. Who Returns What? 2.days.fromToday.at(4.pm) • 4.pm = Integer • At • Accepts Integer • = Calendar • fromToday = Calendar • Days = Integer • 2 = Integer 2007 JavaOneSM Conference | Session TS-1589 | 29
  • 30. Builders in Groovy • Builders make it much easier to build structures • XML documents • Swing user interfaces • Built using a fluent interface • Demo • Generating XML schema and POJO from a database schema 2007 JavaOneSM Conference | Session TS-1589 | 30
  • 31. Groovy: Calendar • The goal • Create an appointment calendar using DSLs • Demonstrates • Open classes • Closures • Loose syntax rules • Demo • Appointment.groovy • AppointmentCalendar.groovy • IntegerWithTimeSupport.groovy • AppointmentCalendarDemo.groovy 2007 JavaOneSM Conference | Session TS-1589 | 31
  • 32. Building Internal DSLs In Ruby 2007 JavaOneSM Conference | Session TS-1589 | 32
  • 33. Ruby • Ruby allows you to take DSL writing much further • Ruby features that enable DSLs • True open classes • Closures • Really flexible syntax rules 2007 JavaOneSM Conference | Session TS-1589 | 33
  • 34. Time DSL in Ruby • Goal • Support time ranges in Ruby • Demo • time_dsl.rb • time_dsl_test.rb 2007 JavaOneSM Conference | Session TS-1589 | 34
  • 35. Ruby Calendar • Our calendar example in Ruby • Demo • calendar_fluent.rb • Functionally the same as the Groovy one • Cleaner syntax • Less cruft • True open classes 2007 JavaOneSM Conference | Session TS-1589 | 35
  • 36. Building External DSLs 2007 JavaOneSM Conference | Session TS-1589 | 36
  • 37. Language Workbenches • A language workbench is a tool that supports Language oriented programming • Today’s language workbenches • Intentional Software (developed by Simonyi) • Software factories (developed by Microsoft) • Meta Programming System (developed by JetBrains) 2007 JavaOneSM Conference | Session TS-1589 | 37
  • 38. Compilation Cycle (Since CS-101) 2007 JavaOneSM Conference | Session TS-1589 | 38
  • 39. “Post-IntelliJ” IDEs • First tool that allowed you to edit against the abstract syntax tree instead of text • How refactoring and other intelligent support works 2007 JavaOneSM Conference | Session TS-1589 | 39
  • 40. Workbenches 2007 JavaOneSM Conference | Session TS-1589 | 40
  • 41. Language Workbenches • Editable representation is a projection of the abstract representation • Abstract representation has to be comfortable with errors and ambiguities 2007 JavaOneSM Conference | Session TS-1589 | 41
  • 42. JetBrains MPS 2007 JavaOneSM Conference | Session TS-1589 | 42
  • 43. DSL Best Practices 2007 JavaOneSM Conference | Session TS-1589 | 43
  • 44. Start with the End • When using a flexible base language, envision the perfect result • The Rake napkin 2007 JavaOneSM Conference | Session TS-1589 | 44
  • 45. Test, Test, Test! • Writing the DSL is the tricky part • Using it should be easy • Otherwise you’ve made some mistakes • Test all the small parts 2007 JavaOneSM Conference | Session TS-1589 | 45
  • 46. The Problem Domain • Keep it as cohesive as possible • Don’t try to write the entire universe in your DSL • Better off using a bunch of very specific DSLs • JetBrains and the way they are using MPS 2007 JavaOneSM Conference | Session TS-1589 | 46
  • 47. DSLs • A huge competitive advantage • All your code is abstracted at the problem domain • Harder to write, easier to maintain • Show your code to your business analysts for verification 2007 JavaOneSM Conference | Session TS-1589 | 47
  • 48. Questions? Samples and slides at www.nealford.com Neal Ford www.nealford.com nford@thoughtworks.com memeagora.blogspot.com This work is licensed under a Creative Commons Attribution-ShareAlike 2.5 License: http://creativecommons.org/licenses/by-sa/2.5/ 2007 JavaOneSM Conference | Session TS-1589 |
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