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Extending JavaAnd Developing DSLsWith JetBrains MPSKonstantin SolomatovJetBrainsLead 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

Charisma – bug tracking system Completely developed with MPS Used internally EAP 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