ReluxScript Language Specification

Version: 0.9.0 Status: Draft Target Platforms: Babel (JavaScript) & SWC (Rust/WASM)

Overview

ReluxScript is a domain-specific language for writing AST transformation plugins that compile to both Babel (JavaScript) and SWC (Rust). It enforces a strict visitor pattern with explicit ownership semantics that map cleanly to both garbage-collected and borrow-checked runtimes.

Design Philosophy

• Strict Visitor, Loose Context: Enforces Rust-like VisitMut pattern
• Immutable by Default: All mutations must be explicit
• No Path Magic: No implicit parent traversal; state must be tracked explicitly
• Unified AST: Subset of nodes common to ESTree (Babel) and swc_ecma_ast
• Clone-to-Own: Explicit .clone() required for value extraction

Vector Alignment Principle

ReluxScript finds the intersection of JavaScript and Rust capabilities, not the union. Code that compiles must be semantically valid in both targets.

This means:

• ✅ What compiles will work on both platforms
• ✅ No surprises, no "works in Babel but not SWC"
• ✅ Predictable, reliable transformations

Complete Specification

For the full language specification including:

• Type system details
• Complete AST node mappings
• Module system
• Writer API for transpilers
• Error handling with Result<T, E>
• Advanced patterns (traverse, verbatim blocks, program hooks)

See the complete specification in the repository: reluxscript-specification.md

Quick Reference

Plugin Structure

plugin MyPlugin {
    // Visitor methods
    fn visit_call_expression(node: &mut CallExpression, ctx: &Context) {
        // transformation logic
    }
}

Common Patterns

Node Replacement:

*node = Statement::empty();

Pattern Matching:

if matches!(node.callee, "console.log") {
    // matched
}

Error Handling:

fn process() -> Result<(), Str> {
    let ast = parser::parse_file("file.tsx")?;
    Ok(())
}

Type System

ReluxScript	Babel (JS)	SWC (Rust)
Str	string	String
i32	number	i32
bool	boolean	bool
Vec<T>	Array	Vec<T>
Option<T>	T | null	Option<T>
Result<T,E>	{ok,value,error}	Result<T,E>

Next Steps

• Core Concepts
• Types Deep Dive
• Pattern Matching
• AST Node Reference