Oleksandr Kozachuk
e963e636d3
CI / check (push) Has been cancelled
A recursive Forth word almost always opens with a guard that returns early, so every leaf of the recursion costs a call whose whole body is that test. `Call(self)` now compiles as `<guard> IF <what the guard returns> ELSE Call(self) THEN`, which is what the callee would have done on entry anyway. Half of fib's nodes are leaves: Fibonacci(25) 356 -> 237 us, 1.24x sf64 -> 0.83x, so all five benchmarks now beat it. The guard runs twice along the recursive path, hence the bounds: at most six effect-free operations, at most four call sites, never a tail call. WS-018.
103 lines
5.2 KiB
Markdown
103 lines
5.2 KiB
Markdown
# WAFER Project Conventions
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## What is WAFER?
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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, per-region stack-to-local promotion with DO/BEGIN loop and IF support, self-recursive direct calls, a typed calling convention for words with a known stack effect, self-guard expansion for recursive words, consolidation). Beats gforth on all benchmarks in release mode (3-20x), and SwiftForth `sf64` on all five. Includes a browser-based REPL via wasm-pack.
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## Architecture
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- Each Forth word compiles to its own WASM module via `wasm-encoder`
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- Modules share memory, globals (dsp/rsp/fsp), and a function table via runtime imports
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- IR-based compilation: Forth -> `Vec<IrOp>` -> WASM codegen -> runtime instantiation
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- Dictionary: linked-list in a `Vec<u8>` buffer simulating WASM linear memory
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- Primitives: either IR-based (compiled to WASM) or host functions (closures via `HostFn`)
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- **Runtime trait**: `ForthVM<R: Runtime>` is generic over the execution backend
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- `NativeRuntime` (wasmtime) -- CLI, tests, AOT compilation
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- `WebRuntime` (js-sys) -- browser REPL via wasm-pack
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## Crate Structure
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- `crates/core` -- compiler, optimizer, codegen, dictionary, runtime traits, outer interpreter
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- `crates/cli` -- CLI REPL with rustyline, `wafer build`/`wafer run` commands
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- `crates/web` -- browser REPL (wasm-bindgen entry point, WebRuntime, HTML/CSS/JS frontend)
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## Key Files
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- `crates/core/src/outer.rs` -- `ForthVM<R: Runtime>`: outer interpreter, compiler, all primitives
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- `crates/core/src/runtime.rs` -- `Runtime` + `HostAccess` traits (execution backend abstraction)
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- `crates/core/src/runtime_native.rs` -- `NativeRuntime`: wasmtime implementation (behind `native` feature)
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- `crates/core/src/codegen.rs` -- IR-to-WASM translation, module generation
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- `crates/core/src/dictionary.rs` -- Dictionary data structure with create/find/reveal
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- `crates/core/src/ir.rs` -- IrOp enum (the intermediate representation)
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- `crates/core/src/memory.rs` -- Memory layout constants (stack regions, dictionary base, etc.)
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- `crates/core/src/optimizer.rs` -- IR optimization passes (peephole, fold, inline, DCE, etc.)
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- `crates/core/src/config.rs` -- WaferConfig: unified optimization configuration
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- `crates/core/src/consolidate.rs` -- Consolidation recompiler (single-module direct calls)
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- `crates/core/boot.fth` -- Bootstrap Forth definitions loaded at startup
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- `crates/cli/src/main.rs` -- CLI REPL with rustyline
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- `crates/web/src/lib.rs` -- `WaferRepl` wasm-bindgen entry point
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- `crates/web/src/runtime_web.rs` -- `WebRuntime`: browser WebAssembly API via js-sys
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- `crates/web/www/` -- Frontend (index.html, style.css, app.js)
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## Feature Flags (wafer-core)
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- `default = ["native"]` -- includes wasmtime, NativeRuntime, runner, export, etc.
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- `native` -- enables `dep:wasmtime` and all native-only modules
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- No features -- pure Rust only (dictionary, IR, optimizer, codegen, outer interpreter). Used by `wafer-web`.
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## Adding a New Word
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**IR primitive** (simple stack/arithmetic/logic -- preferred when possible):
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```rust
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self.register_primitive("WORD_NAME", false, vec![IrOp::Dup, IrOp::Mul])?;
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```
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**Host function** (needs Rust logic -- I/O, dictionary manipulation, complex stack access):
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```rust
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let shared_state = Arc::clone(&self.some_field);
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let func: HostFn = Box::new(move |ctx: &mut dyn HostAccess| {
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let sp = ctx.get_dsp();
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let val = ctx.mem_read_i32(sp);
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// ... logic using ctx for memory/global access ...
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ctx.set_dsp(sp + CELL_SIZE);
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Ok(())
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});
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self.register_host_primitive("WORD_NAME", false, func)?;
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```
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**Special interpreter token** (defining words like VARIABLE, CONSTANT, CREATE):
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Handle in `interpret_token_immediate()` or `compile_token()` as a special case.
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## Code Style
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- `cargo fmt --all` and `cargo clippy --workspace` must pass with no warnings
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- Every public function needs a doc comment
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- Use `thiserror` for error types in core crate, `anyhow` for CLI
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- Prefer returning `Result` over panicking
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## Testing
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- Run `cargo test --workspace` before committing (currently 608 unit + 1 benchmark + 12 compliance + 9 comparison + 5 crypto)
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- Forth 2012 compliance: `cargo test -p wafer-core --test compliance`
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- Cross-engine comparison (vs gforth): `cargo test -p wafer-core --test comparison`
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- Performance benchmarks (release mode): `cargo test -p wafer-core --test comparison -- --nocapture --ignored`
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- Test helper in outer.rs: `eval_output("forth code")` returns printed output as String
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- Test helper: `eval_stack("forth code")` returns data stack as Vec<i32>
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## Web REPL
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- Build: `cd crates/web && wasm-pack build --target web --out-dir www/pkg`
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- Serve: `python3 -m http.server -d crates/web/www 8080`
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- Open: `http://localhost:8080/`
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- Dev build (faster, unoptimized): `wasm-pack build --target web --dev --out-dir www/pkg`
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## Key Principles
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1. Correctness first, performance second
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2. Maximize Forth, minimize Rust (self-hosting goal -- not yet started)
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3. Test-driven: if it's not tested, it doesn't work
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4. Every word set at 100% compliance before moving to the next
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5. Never break existing tests
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