geolog-zeta-fork/notes/003-project-status.md

# Project Status

**Version:** 0.1.0 (Early stage, but functional)

---

## Codebase Size

| What | Count |
|------|-------|
| Rust source code | ~30,000 lines |
| Test code | ~8,000 lines |
| Example `.geolog` files | ~2,300 lines across 30 files |
| Source files | 84 |
| Unit tests | 137 (all passing) |
| Integration tests | 31 (all passing) |

---

## What Works Well

These features are complete and reliable:

### Core Engine
- **Parser** — reads `.geolog` files, gives helpful error messages
- **Type checker** — catches mistakes like using undefined sorts
- **Chase algorithm** — derives facts from rules correctly
- **Equality handling** — when rules say `x = y`, elements are properly merged

### Examples That Run
```bash
cargo run -- examples/geolog/graph.geolog        # Simple directed graph
cargo run -- examples/geolog/preorder.geolog     # Reflexive, transitive relation
cargo run -- examples/geolog/transitive_closure.geolog  # Shows chase in action
cargo run -- examples/geolog/category.geolog     # Category theory basics
```

### Interactive Features
- REPL with command history
- Inspect any theory or instance
- Run chase interactively
- Save/load with version history

---

## What Mostly Works

These features work but have limitations:

### Parameterized Theories
You can define theories that depend on other instances:

```geolog
theory (N : PetriNet instance) Marking {
  token : Sort;
  token/of : token -> N/P;  // References N's places
}
```

**Limitation:** Nested instances (instances inside instances) only partially work.

### Model Search
The solver can find models satisfying axioms, but:
- Works best for small models
- Some search strategies are incomplete
- No timeout handling

---

## Known Gaps

### Things That Don't Work Yet

| Feature | Status |
|---------|--------|
| Product types in conclusions | Functions returning records don't fully work |
| Existentials over products | `exists p : [x:M, y:M]. ...` fails |
| Field projections in equations | `x.field = y` doesn't compile |

### Example of What Fails

```geolog
// This works:
forall x : M. |- exists y : M. f(x) = y

// This doesn't work (product sort in existential):
forall x : M. |- exists p : [a:M, b:M]. g(x) = p
```

### Silent Failures

When the tensor compiler can't handle an axiom, it **silently skips it**. This can be confusing — your axiom looks fine but nothing happens.

```geolog
// This axiom might be silently skipped if it has unsupported patterns:
ax/complex : forall x. premise |- [a: x, b: x] some_relation;
// No error, but also no effect
```

---

## TODOs in the Code

These are marked in the source with `// TODO`:

| Location | What's Missing |
|----------|----------------|
| `src/repl.rs:84` | Theory type not fully stored in metadata |
| `src/overlay.rs:380` | Copying functions between structures |
| `src/store/query.rs:61` | Batch loading for better performance |
| `src/store/instance.rs` | External references between instances |
| `src/query/to_relalg.rs` | Some relational operators |

---

## Test Coverage

### What's Tested

| Area | Tests |
|------|-------|
| Type checking | 14 unit tests |
| Chase algorithm | Comprehensive unit tests |
| Parser | 4 unit tests + snapshot tests |
| Examples | 31 integration tests (one per example file) |
| Random inputs | 11 property-based test suites |

### Running Tests

```bash
cargo test              # Run all tests
cargo test unit_chase   # Run only chase tests
cargo test --release    # Run with optimizations (faster)
```

### Fuzzing

The `fuzz/` directory has fuzzing targets that generate random inputs to find crashes:

```bash
cargo +nightly fuzz run fuzz_parser
```

---

## What's Being Worked On

According to code comments and structure:

1. **Lean4 formalization** — Mathematical proofs about correctness (in `proofs/`)
2. **Better disjunction handling** — Currently fires both branches, should choose one
3. **Query plan improvements** — More efficient execution