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Extending JavaAnd Developing DSLsWith Open Source Language Workbench JetBrains MPS Konstantin Solomatov

JetBrainsLead Developer for JetBrains MPS Project

Agenda

Extending languages. Why bother? Problems and solutions

Composability Language support

MPS’ approach Idea behind it Hands-on demo

MPS & domain-specific languages

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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

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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

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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

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MPS DEMO

Closure & UI Language samples.

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Agenda

Extending Languages. Why bother? Problems and Solutions

Composability Language support

MPS’ Approach Idea behind it Hands-on Demo

MPS & Domain-Specific Languages

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Composability

Definition:

Components are composable when they can be used together even if created by different parties

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ComposabilityDesired Goal

Java Libraries

Hibernate Spring Joda Time

Java Extensions

DB Language DI Language Dates Language

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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

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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}”;

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Language SupportRequirements Generic infrastructure

Abstract grammar Type system Compiler Etc.

IDE infrastructure Editor Error highlighting Refactoring Version control Etc.

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Language SupportProblems Time- and resource-consuming task

Complicated algorithms for processing code Highly qualified developers required

Resulting infrastructure composability Type systems to be compatible with different

extensions Refactorings should support potential extensions Etc.

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Existing SolutionsPros & Cons

ComposabilityLanguage

Infrastructure

LISP Yes No

Internal DSLs in Ruby / Groovy Yes No

XText Framework No Yes

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Common Problem

Existing solutions provide: Either composable language extensions Or a decent infrastructure Not both

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Agenda

Extending Languages. Why bother? Problems and Solutions

Composability Language support

MPS’ Approach Idea behind it Hands-on Demo

MPS & Domain-Specific Languages

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Our Solution to the Problem

JetBrains MPS

Workbench for defining and extending languages

IDE for new languages and extensions

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Idea Behind It

Text-based grammars lead to ambiguities

Another approach needed

MPS works with Abstract Syntax Tree directly

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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

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Idea Behind ItProjectional Editor

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Each node of a syntax tree has its projection in the MPS Editor

Idea Behind ItProjectional Editor

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Each node – in a dedicated cell A node is shown in its text/symbol representation Instantly synchronized editor and syntax tree

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

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MPS DEMO

Projectional editor in use.

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Idea Behind ItLanguage Support User-defined language infrastructure

Abstract grammar Type system Editor Compiler Etc.

Programming assistance Completion Find usages Rename Etc.

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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.)

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Hands-On DemoGoal

Java

ReadWriteLock l = …l.readLock().lock();try { //code} finally {

l.readLock().unlock();

}

Java + Extension

ReadWriteLock l = …read (l) { //code}

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Hands-On DemoWorkflow We will define

Structure Editor Typesystem Generator

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MPS DEMO

Adding lock statement to Java

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Agenda

Extending Languages. Why bother? Problems and Solutions

Composability Language support

MPS’ Approach Idea behind it Hands-on Demo

MPS & Domain-Specific Languages

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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

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Domain-Specific LanguagesExample

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Existing Applications

YouTrack – bug tracking system Completely developed with MPS Used internally Beta program

Languages for Web Development DNQ Webr Spring language

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Licensing/Pricing

Almost fully open-sourced Apache 2.0 License

MPS is absolutely FREE

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Q & A

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More info

http://www.jetbrains.com/mps - MPS pagehttp://blogs.jetbrains.com/mps - MPS blog

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Konstantin Solomatovkonstantin.solomatov@jetbrains.com

Lead Developer for JetBrains MPS Projecthttp://www.jetbrains.com/mps

Thank You