Posts Tagged ‘CédricChampeau’
[DevoxxFR2013] Groovy and Statically Typed DSLs
Lecturer
Guillaume Laforge manages the Groovy project and leads JSR-241 for its standardization. As Vice President of Technology at G2One, he delivers services around Groovy/Grails. Co-author of “Groovy in Action,” he evangelizes at global conferences.
Cédric Champeau contributes to Groovy core at SpringSource (VMware division). Previously at Lingway, he applied Groovy industrially in DSLs, scripting, workflows.
Abstract
Guillaume Laforge and Cédric Champeau explore Groovy’s evolution in crafting statically typed domain-specific languages (DSLs). Building on runtime metaprogramming, Groovy 2.1 introduces compile-time features for type safety without sacrificing flexibility. They demonstrate extensions, AST transformations, and error reporting, culminating in advanced builders surpassing Java’s checks, illustrating implications for robust, expressive DSL design.
Groovy’s DSL Heritage: Dynamic Foundations and Metaprogramming
Laforge recaps Groovy’s DSL prowess: flexible syntax, runtime interception (invokeMethod, getProperty), closures for blocks.
Examples: method missing for fluent APIs, expando meta-classes for adaptations.
This dynamism accelerates development but risks runtime errors. Groovy 2 adds optional static typing (@TypeChecked), clashing initially with dynamic DSLs.
Bridging Static and Dynamic: Compile-Time Extensions
Champeau introduces Groovy 2.1’s static compile-time metaprogramming. @CompileStatic enables type checking; extensions handle DSL specifics.
Trait-like extensions via extension modules: add methods to classes statically.
// Extension class
class HtmlExtension {
static NodeBuilder div(Element self, Closure c) { /* build */ }
}
Register in META-INF, usable in typed code with error propagation.
This preserves DSL fluency under static compilation.
AST Transformations for Deeper Integration
Custom AST transformations inject code during compilation. @Builder variants, delegation.
For DSLs: transform method calls into builders, validate arguments statically.
Example: markup builder with type-checked HTML generation, reporting mismatches at compile-time.
Champeau details global transformations for cross-cutting concerns.
Advanced Type Checking: Custom Error Reporting and Beyond Java
Laforge showcases @TypeChecked with custom type checkers. Override doVisit for context-specific rules.
@TypeChecked
void script() {
html {
div(id: 'main') { /* content */ }
}
}
Checker ensures div accepts valid attributes, closures; errors reference user code lines.
Groovy exceeds Java: infer types in dynamic contexts, enforce domain rules unavailable in Java.
Builder Patterns and Real-World Applications
Demonstrate HTML DSL: nested closures build node trees, statically verified.
Grails integration: apply to GSPs for compile-time validation.
Champeau notes Grails’ metaprogramming complexity as ideal testbed—getProperty, MOP, AST all in play.
Implications for DSL Engineering: Safety, Productivity, Evolution
Static typing catches errors early, aids IDE support (autocompletion, refactoring). Dynamic essence retained via extensions.
Trade-offs: setup complexity; mitigated by community modules.
Future: deeper Grails incorporation, enhanced tooling.
Laforge and Champeau position Groovy as premier for type-safe yet expressive DSLs, blending agility with reliability.