This document proposes an approach called Syntax Classes for defining domain-specific languages (DSLs) in an extensible way within Java. It allows new languages to be defined as classes that implement a standard interface for abstract syntax trees. This provides a modular and conservative approach to DSL definition that fully integrates new languages into the Java platform and tooling. Syntax classes provide a standardized mechanism for defining the syntax, static processing, and execution of DSL code through grammar definitions, AST manipulation, and language import capabilities. Examples of DSL constructs that could be defined include vector operations, data mapping, and entity definitions.

1. 1Beyond Annotations:A Proposal for Extensible Java(XJ)Tony Clark, Thames Valley UniversityPaul Sammut, HSBCJames Willans, Cetevatony.clark@tvu.ac.ukwww.ceteva.com/home/tony.html

2. 2Domain Specific LanguagesAims: to provide a tailored language; to support mixed languages; language evolution.Pros: declarative; maintenance; reuse; verificationCons: specialist skills; no standard technology; lack of integration.Technologies: macros; pre-processing; roll-your-own; chained calls.

3. 3DSLs: Technology ProblemsCommunication: distributing new languages.Integration: IDEs; Analysis Tools.Modularity: clear definition of syntax and semantics.DSL Types: Internal and External.Syntax (concrete and abstract): standard extension mechanisms.

4. 4DSLs: An OO ProposalSyntax ClassesModular: class-based language constructs.Conservative: extends base language.Fully Integrated: static; dynamic; IDE.Standardized: syntax extension; AST manipulation; static processing; execution.

5. 5Syntax Classes: DSL Architecturepackage p.q;import language java.syntax.grammar;class mylang implements java.syntax.AST { ... @grammar { // language definition }}import language p.q.mylang;class C { void m(...) { ... @mylang { // Syntax and semantics defined // by class mylang. } }} modular.

6. nesting.

7. conservative.

8. standard.6Example DSL Constructspublic Vector<Integer> add1(Vector<Integer> nums) { return @Cmp(x + 1) { int x <- nums };}@Reader CallReader { map(SVCL,ServiceCall) 4-18:CustomerName 19-23:CustomerID 24-27:CallTypeCode 28-35:DataOfCallString end map(USGE,Usage) 4-8:CustomerID 9-22:CustomerName 30-30:Cycle 31-36:ReadDate end do ServiceCall Usage }@EntityBean Order persistAs "ORDER_TABLE" { private int id persistAs "ORDER_ID" (get,set); private int address persistAs "SHIPPING_ADDRESS" (get,set);}

9. 7Syntax Classes: TechnologiesGrammars: basic library; synthesizes abstract syntax; various languages possible.AST interface: factories; types; eval; compile;… Quasi-quotes: working with concrete/abstract syntax: [| <o>.m(<a>,1) |]Language: import; @; grammar; [| … |].

10. 8ReviewImplemented in XMF: commercial tool; open-source (www.ceteva.com) Superlanguages book: (www.ceteva.com/docs/Superlanguages.pdf) DSLs require standard technology.Open up Java to define new languages.Issues: language interaction; IDE support; analysis tool requirements.

11. 9StatementNew languages and constructs can/should implement a standard interface to facilitate program analysis.