WAFER/CLAUDE.md

WAFER Project Conventions

What is WAFER?

WAFER (WebAssembly Forth Engine in Rust) is an optimizing Forth 2012 compiler targeting WebAssembly. Currently a working Forth system with 200+ words, JIT compilation, 12 word sets at 100% compliance, and a full optimization pipeline (peephole, constant folding, inlining, strength reduction, DCE, tail calls, stack-to-local promotion with loop/IF support, self-recursive direct calls, consolidation). Beats gforth on all benchmarks in release mode. Includes a browser-based REPL via wasm-pack.

Architecture

• Each Forth word compiles to its own WASM module via wasm-encoder
• Modules share memory, globals (dsp/rsp/fsp), and a function table via runtime imports
• IR-based compilation: Forth -> Vec<IrOp> -> WASM codegen -> runtime instantiation
• Dictionary: linked-list in a Vec<u8> buffer simulating WASM linear memory
• Primitives: either IR-based (compiled to WASM) or host functions (closures via HostFn)
• Runtime trait: ForthVM<R: Runtime> is generic over the execution backend
  • NativeRuntime (wasmtime) -- CLI, tests, AOT compilation
  • WebRuntime (js-sys) -- browser REPL via wasm-pack

Crate Structure

• crates/core -- compiler, optimizer, codegen, dictionary, runtime traits, outer interpreter
• crates/cli -- CLI REPL with rustyline, wafer build/wafer run commands
• crates/web -- browser REPL (wasm-bindgen entry point, WebRuntime, HTML/CSS/JS frontend)

Key Files

• crates/core/src/outer.rs -- ForthVM<R: Runtime>: outer interpreter, compiler, all primitives
• crates/core/src/runtime.rs -- Runtime + HostAccess traits (execution backend abstraction)
• crates/core/src/runtime_native.rs -- NativeRuntime: wasmtime implementation (behind native feature)
• crates/core/src/codegen.rs -- IR-to-WASM translation, module generation
• crates/core/src/dictionary.rs -- Dictionary data structure with create/find/reveal
• crates/core/src/ir.rs -- IrOp enum (the intermediate representation)
• crates/core/src/memory.rs -- Memory layout constants (stack regions, dictionary base, etc.)
• crates/core/src/optimizer.rs -- IR optimization passes (peephole, fold, inline, DCE, etc.)
• crates/core/src/config.rs -- WaferConfig: unified optimization configuration
• crates/core/src/consolidate.rs -- Consolidation recompiler (single-module direct calls)
• crates/core/boot.fth -- Bootstrap Forth definitions loaded at startup
• crates/cli/src/main.rs -- CLI REPL with rustyline
• crates/web/src/lib.rs -- WaferRepl wasm-bindgen entry point
• crates/web/src/runtime_web.rs -- WebRuntime: browser WebAssembly API via js-sys
• crates/web/www/ -- Frontend (index.html, style.css, app.js)

Feature Flags (wafer-core)

• default = ["native"] -- includes wasmtime, NativeRuntime, runner, export, etc.
• native -- enables dep:wasmtime and all native-only modules
• No features -- pure Rust only (dictionary, IR, optimizer, codegen, outer interpreter). Used by wafer-web.

Adding a New Word

IR primitive (simple stack/arithmetic/logic -- preferred when possible):

self.register_primitive("WORD_NAME", false, vec![IrOp::Dup, IrOp::Mul])?;

Host function (needs Rust logic -- I/O, dictionary manipulation, complex stack access):

let shared_state = Arc::clone(&self.some_field);
let func: HostFn = Box::new(move |ctx: &mut dyn HostAccess| {
    let sp = ctx.get_dsp();
    let val = ctx.mem_read_i32(sp);
    // ... logic using ctx for memory/global access ...
    ctx.set_dsp(sp + CELL_SIZE);
    Ok(())
});
self.register_host_primitive("WORD_NAME", false, func)?;

Special interpreter token (defining words like VARIABLE, CONSTANT, CREATE): Handle in interpret_token_immediate() or compile_token() as a special case.

Code Style

• cargo fmt --all and cargo clippy --workspace must pass with no warnings
• Every public function needs a doc comment
• Use thiserror for error types in core crate, anyhow for CLI
• Prefer returning Result over panicking

Testing

• Run cargo test --workspace before committing (currently 431 unit + 1 benchmark + 11 compliance + 9 comparison)
• Forth 2012 compliance: cargo test -p wafer-core --test compliance
• Cross-engine comparison (vs gforth): cargo test -p wafer-core --test comparison
• Performance benchmarks (release mode): cargo test -p wafer-core --test comparison -- --nocapture --ignored
• Test helper in outer.rs: eval_output("forth code") returns printed output as String
• Test helper: eval_stack("forth code") returns data stack as Vec

Web REPL

• Build: cd crates/web && wasm-pack build --target web --out-dir www/pkg
• Serve: python3 -m http.server -d crates/web/www 8080
• Open: http://localhost:8080/
• Dev build (faster, unoptimized): wasm-pack build --target web --dev --out-dir www/pkg

Key Principles

1. Correctness first, performance second
2. Maximize Forth, minimize Rust (self-hosting goal -- not yet started)
3. Test-driven: if it's not tested, it doesn't work
4. Every word set at 100% compliance before moving to the next
5. Never break existing tests