Rail

Rail is a domain-specific language for model railroad automation. It compiles to EXRAIL, the scripting language for DCC-EX CommandStation controllers.

Rail lets you describe layout behavior — turnouts, signals, sensors, and automation logic — in a high-level syntax that compiles directly to the EXRAIL commands your CommandStation executes.

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For Model Railroaders

Quick Start

// hello.rail — blink a signal's headlight
startup {
    pin PB7 = output
    loop {
        on PB7
        delay 1000
        off PB7
        delay 1000
    }
}

Compile with:

railc hello.rail -o hello.exrail

Upload hello.exrail to your DCC-EX CommandStation.

Features

• Declarative syntax — describe what you want, not how
• Safe by default — compile-time checks catch wiring errors before they reach your layout
• DCC-EX native — compiles directly to EXRAIL, no runtime needed
• Procedural automation — define reusable behaviors with parameters
• Composite types — model turnouts, signals, and sensors as structured objects

Installation

cargo install railc

Requires Rust nightly. See CONTRIBUTING.md for build instructions.

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For Compiler Enthusiasts

Architecture

The Rail compiler transforms source text through several intermediate representations:

Source (.rail)
    │
    ▼
┌──────────────┐
│   Lexer      │  logos-based tokenizer
├──────────────┤
│   Parser     │  chumsky combinator parser → AST
├──────────────┤
│   Resolver   │  two-phase name resolution → typed DefIds
├──────────────┤
│ Type Checker │  type inference → HIR (High-level IR)
├──────────────┤
│     MIR      │  CFG-based Mid-level IR
├──────────────┤
│  Optimizer   │  constant folding, DCE, propagation
├──────────────┤
│   Codegen    │  (planned) → EXRAIL output
└──────────────┘

Repository Structure

rail/
├── Cargo.toml          # Workspace root
├── rail-core/          # Compiler library
│   ├── src/
│   │   ├── lexer.rs    # Tokenizer
│   │   ├── parser/     # Parser combinators (11 files)
│   │   ├── semantic/   # Resolution, type checking, HIR
│   │   └── optimizer/  # MIR types, lowering, passes
│   └── Cargo.toml
├── railc/              # CLI binary (placeholder)
│   └── src/
└── docs/               # Language documentation

Build from Source

git clone https://github.com/pontes/rail
cd rail
cargo build --release

Run Tests

cargo test --workspace

All tests must pass. The project maintains 252+ tests with strict clippy linting.

Project Status

Rail is currently in active development as a CS bachelor's thesis project. The compiler pipeline (lex → parse → resolve → type-check → HIR → MIR → optimize) is complete. EXRAIL codegen is the next major phase.

Contributing

See CONTRIBUTING.md for guidelines.

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License

This project is dual-licensed under MIT and Apache 2.0.