Extending Java And Developing DSLs With JetBrains MPS

1. Extending JavaAnd Developing DSLsWith JetBrains MPS Konstantin Solomatov JetBrains Lead Developer for JetBrains MPS Project 1

2. Agenda • Extending languages. Why bother? • Problems and solutions • Composability • Language support • MPS’ approach • Idea behind it • Hands-on demo • MPS & domain-specific languages 2

3. Why Bother? • Specific domains = specific entities • Drawbacks of general-purpose languages: • Limited set of generic constructs • Domains are described too verbosely • Low code maintainability • Domain-specific extensions • Higher abstraction level • Higher maintainability 3

4. Implicit Language Extensions • Domain-specific constructs in Java: • synchronized block in Java • enhanced for in Java • typesafe enums in Java • Desired constructs: • closures • yield • better support for regexps • whatever else you are missing 4

5. MPS DEMO Closure & UI Language samples. 5

6. Language Extensions • Existing extensions • Cover domain-specific needs • Are built into existing languages • Further extensions • Hard to integrate • Too long to wait until JCP accepts them  • Risks of incompatibility 6

7. Agenda • Extending Languages. Why bother? • Problems and Solutions • Composability • Language support • MPS’ Approach • Idea behind it • Hands-on Demo • MPS & Domain-Specific Languages 7

8. Composability Definition: Components are composable when they can be used together even if created by different parties 8

9. ComposabilityDesired Goal Java Libraries Hibernate Spring Joda Time Java Extensions DB Language DI Language Dates Language 9

10. ComposabilityLibraries vs. Extensions • Libraries are composable: • Java + Hibernate => OK • Java + Spring => OK • Java + Hibernate, Spring => OK • Language extensions are not • Java + extension A => OK • Java + extension B => OK • Java + extensions A, B => possible ambiguity 10

11. ComposabilityGrammar Ambiguity Sample With String Interpolation Extension “A”: int resultsCount = <some_code>;string s = “Found ${resultCount} results”; Extension “B”: int resultCount = <some_code>;string t = “Found {resultCount} results”; “A”+“B” => ambiguity for the compiler: string a = “Account balance is ${balance}”; 11

12. Language SupportRequirements • Generic infrastructure • Abstract grammar • Type system • Compiler • Etc. • IDE infrastructure • Editor • Error highlighting • Refactoring • Version control • Etc. 12

13. Language SupportProblems • Time- and resource-consuming task • Complicated algorithms for processing code • Highly qualified developers required • Resulting infrastructure compatibility • Type systems to be compatible with different extensions • Refactorings should support potential extensions • Etc. 13

14. Existing SolutionsPros & Cons 14

15. Common Problem • Existing solutions provide: • Either composable language extensions • Ora decent infrastructure • Not both 15

16. Agenda • Extending Languages. Why bother? • Problems and Solutions • Composability • Language support • MPS’ Approach • Idea behind it • Hands-on Demo • MPS & Domain-Specific Languages 16

17. Our Solution to the Problem • JetBrains MPS • Workbench for defining and extending languages • IDE for new languages and extensions 17

18. Idea Behind It Text-based grammars lead to ambiguities Another approach needed MPS works with Abstract Syntax Tree directly 18

19. Idea Behind ItEditing Abstract Syntax Tree • Former attempts • Diagram-based editing • Limited domain of application • MPS solution • Keeps user in habitual environment • Supports text-like editing 19

20. Idea Behind ItProjectional Editor • Each node of a syntax tree has its projectionin the MPS Editor 20

21. Idea Behind ItProjectional Editor • Each node – in a dedicated cell • A node is shown in its text/symbol representation • Instantly synchronized editor and syntax tree 21

22. Idea Behind ItProjection vs. Text • Text-like projectional editor • Has its pros & cons • Reasonable learning curve: approx. 2 weeks 22

23. MPS DEMO Projectional editor in use. 23

24. Idea Behind ItLanguage Support • User-defined language infrastructure • Abstract grammar • Type system • Editor • Compiler • Etc. • Programming assistance • Completion • Find usages • Rename • Etc. 24

25. Idea Behind It Existing Languages & Extensions • Java™ re-implemented with MPS + Extensions • Collections language • Dates language • Closures language • Regexp language • Etc. • Language definition languages • Implemented with themselves i.e. bootstrapped • Misc languages (XML, etc.) 25

26. Hands-On DemoGoal Java ReadWriteLock l = … l.readLock().lock(); try { //code } finally { l.readLock().unlock(); } Java + Extension ReadWriteLock l = … read (l) { //code } 26

27. Hands On DemoWorkflow • We will define • Structure • Editor • Typesystem • Generator 27

28. MPS DEMO Adding lock statement to Java 28

29. Agenda • Extending Languages. Why bother? • Problems and Solutions • Composability • Language support • MPS’ Approach • Idea behind it • Hands-on Demo • MPS & Domain-Specific Languages 29

30. Domain-Specific Languages • MPS suits nicely for creating DSLs • Common language parts can be reused (e.g., expression language) • You can embed general-purpose languages (e.g., Java) inside DSLs 30

31. Domain-Specific LanguagesExample 31

32. Existing Applications • Charisma – bug tracking system • Completely developed with MPS • Used internally • Languages for Web Development • DNQ • Webr • Spring language 32

33. Licensing/Pricing Almost fully open-sourced Apache 2.0 License MPS is absolutely FREE 33

34. Q & A 34

35. More info http://www.jetbrains.com/mps - MPS page http://blogs.jetbrains.com/mps - MPS blog 35

36. Thank You Konstantin Solomatov konstantin.solomatov@jetbrains.com Lead Developer for JetBrains MPS Project http://www.jetbrains.com/mps