geolog-zeta-fork/notes/006-missing-components.md

# Missing Components

*Assuming Geolog's core is mature and stable, what would be needed to make it production-ready?*

---

## Summary

Geolog has a solid **core engine** (parser, type checker, chase, tensor algebra) but is missing everything around it:

- **No way in** — no API, no language bindings
- **No way to scale** — no parallelism, no indexes, no query optimization
- **No way to operate** — no concurrency, no recovery, no monitoring
- **No way to debug** — no logging, no traces, no profiling

It's a well-built engine without a car around it.

---

## 1. Integration & APIs

| Missing | Why It Matters |
|---------|----------------|
| **REST API** | Can't call Geolog from web apps, microservices, or other languages |
| **Language bindings** | No Python, JavaScript, or FFI — Rust-only |
| **LSP (Language Server)** | No IDE autocomplete, error squiggles, go-to-definition |
| **JSON/YAML serialization** | Only binary format (rkyv) — can't inspect data externally |
| **Async API** | All operations block — can't integrate with async runtimes |

### What Integration Would Look Like

```python
# This doesn't exist today
from geolog import Theory, Instance

theory = Theory.parse("""
    theory Graph {
        V : Sort;
        E : Sort;
        src : E -> V;
        tgt : E -> V;
    }
""")

instance = Instance.create(theory)
instance.add_element("V", "alice")
instance.add_element("V", "bob")
instance.add_element("E", "edge1")
instance.set_function("edge1", "src", "alice")
instance.set_function("edge1", "tgt", "bob")

# Run chase and get results as JSON
results = instance.chase()
print(results.to_json())
```

```bash
# REST API that doesn't exist
curl -X POST http://localhost:8080/chase \
  -H "Content-Type: application/json" \
  -d '{"instance": "MyGraph", "max_iterations": 100}'
```

---

## 2. Performance & Scale

| Missing | Why It Matters |
|---------|----------------|
| **Cost-based query optimizer** | No cardinality estimates — can't choose optimal join order |
| **Secondary indexes** | Only RoaringBitmaps — no B-trees for range queries |
| **Parallel execution** | Single-threaded only |
| **Benchmark suite** | No way to track performance regressions |
| **Memory profiling** | No visibility into allocation patterns |

### What Would Struggle

```
Scenario: Theory with 10,000 elements and 50 axioms

Problems:
→ No way to predict which axioms are expensive
→ No parallel chase execution
→ No index to speed up specific lookups
→ No benchmark to know if changes made it slower
```

### What's Needed

```rust
// Cost-based optimizer (doesn't exist)
let plan = optimizer.compile(query);
println!("Estimated cost: {}", plan.estimated_cost());
println!("Join order: {:?}", plan.join_order());

// Parallel chase (doesn't exist)
let results = chase_parallel(axioms, structure, num_threads=4);

// Benchmarks (don't exist)
// benches/chase_benchmark.rs
// benches/tensor_benchmark.rs
```

---

## 3. Solver Intelligence

| Missing | Why It Matters |
|---------|----------------|
| **Search heuristics** | Breadth-first only — no intelligent variable/value ordering |
| **Backtracking** | Can't explore branches — only refines single partial model |
| **Lemma learning** | No conflict-driven learning (CDCL) like modern SAT/SMT solvers |
| **External prover integration** | Can't delegate to Z3, Lean, or Coq |

### Current Behavior

```
Solver tries everything in order:
  x = 1? Try it.
  x = 2? Try it.
  x = 3? Try it.
  ...

No learning from failures.
No "this variable is most constrained, try it first."
```

### What Modern Solvers Do

```
CDCL (Conflict-Driven Clause Learning):
  1. Try x = 1
  2. Conflict detected!
  3. Learn: "x ≠ 1" (add as constraint)
  4. Backtrack and never try x = 1 again

Variable ordering:
  1. Count constraints on each variable
  2. Try most-constrained variable first
  3. Fail fast, prune search space early
```

---

## 4. Reliability & Operations

| Missing | Why It Matters |
|---------|----------------|
| **Multi-user concurrency** | No locking — can't have multiple writers |
| **ACID transactions** | No rollback on failure |
| **Write-ahead log (WAL)** | No crash recovery |
| **Replication** | No distributed deployment |
| **Garbage collection** | Tombstoned elements accumulate forever |
| **Compression** | Data size grows unbounded |

### Production Scenario That Fails

```
User A: :chase BigInstance     (starts running)
User B: :add BigInstance x:V;  (modifies while A is running)

Result: Race condition, possible data corruption
No way to recover if either crashes mid-operation
No way to rollback User B's change if it breaks something
```

### What's Needed

```rust
// Transactions (don't exist)
let tx = store.begin_transaction();
tx.add_element("V", "new_vertex")?;
tx.chase("MyInstance")?;
tx.commit()?;  // Or tx.rollback() on error

// Concurrency control (doesn't exist)
let lock = store.write_lock("MyInstance");
// ... safe modifications ...
drop(lock);

// Crash recovery (doesn't exist)
// WAL ensures operations are durable before acknowledging
```

---

## 5. Developer Experience

| Missing | Why It Matters |
|---------|----------------|
| **Logging framework** | No structured logs for debugging |
| **Interactive debugger** | Can't step through solver decisions |
| **Execution traces** | Can't replay what happened |
| **IDE plugin** | No syntax highlighting, no error squiggles |
| **Tutorials** | Only reference docs, no guided learning |

### Debugging Today

```
> :chase MyInstance
// Something went wrong... but what?
// No logs, no trace, just the final state
// Which axiom fired? Which elements were created? Unknown.
```

### What's Needed

```
// Structured logging (doesn't exist)
[2026-03-19 10:30:01] INFO  chase: Starting chase on MyInstance
[2026-03-19 10:30:01] DEBUG chase: Axiom ax/trans fired with {x: v1, y: v2, z: v3}
[2026-03-19 10:30:01] DEBUG chase: Added relation [x:v1, y:v3] leq
[2026-03-19 10:30:02] INFO  chase: Fixpoint reached after 3 iterations

// Interactive debugger (doesn't exist)
> :debug chase MyInstance
Breakpoint at axiom ax/trans
  Variables: x=v1, y=v2, z=v3
  Action: Add [x:v1, y:v3] leq
(debug) step
(debug) inspect structure
(debug) continue
```

---

## 6. Error Handling

| Missing | Why It Matters |
|---------|----------------|
| **Typed error enums** | All errors are strings — can't handle programmatically |
| **Error recovery suggestions** | "Did you mean X?" doesn't exist |
| **Partial results** | If 90% succeeds, you get nothing |
| **Stack traces** | Limited context for where errors occur |

### Current State

```rust
// All errors are just strings
fn elaborate_theory(...) -> Result<Theory, String>

// Can only display, not handle programmatically
match result {
    Err(msg) => println!("{}", msg),  // That's all you can do
}
```

### What's Needed

```rust
enum GeologError {
    Parse(ParseError),
    Type(TypeError),
    Chase(ChaseError),
    Solver(SolverError),
}

enum ParseError {
    UnexpectedToken { span: Span, found: Token, expected: Vec<Token> },
    UnterminatedString { span: Span },
    // ...
}

enum TypeError {
    UndefinedSort { name: String, span: Span, similar: Vec<String> },
    TypeMismatch { expected: Type, found: Type, span: Span },
    // ...
}

// Now you can handle errors programmatically
match result {
    Err(GeologError::Type(TypeError::UndefinedSort { name, similar, .. })) => {
        println!("Unknown sort '{}'. Did you mean '{}'?", name, similar[0]);
    }
    // ...
}
```

---

## 7. Missing Language Features

| Missing | Why It Matters |
|---------|----------------|
| **Modules/imports** | Can't organize large theories into files |
| **Parameterized axioms** | Can't write generic rules that work across sorts |
| **Arithmetic** | No `x + 1 = y` or `count > 0` |
| **Aggregation** | No `count`, `sum`, `max` over relations |
| **Stratified negation** | No "if NOT X" even in limited safe form |

### What You Can't Express

```geolog
// Modules (don't exist)
import std/graph;
import std/preorder;

// Arithmetic (doesn't exist)
ax/increment : forall x : Nat. |- successor(x) = x + 1;

// Aggregation (doesn't exist)
ax/has_friends : forall p : Person.
    count([f: f] friend_of(p, f)) > 0 |- popular(p);

// Stratified negation (doesn't exist)
ax/lonely : forall p : Person.
    not exists f : Person. friend_of(p, f) |- lonely(p);
```

---

## Priority Ranking

If making Geolog production-ready:

| Priority | Component | Effort | Impact |
|----------|-----------|--------|--------|
| 1 | REST API | Medium | Unlocks all integrations |
| 2 | LSP server | Medium | Makes language usable in IDEs |
| 3 | Structured errors | Low | Enables better tooling |
| 4 | Benchmark suite | Low | Enables performance work |
| 5 | Logging/tracing | Low | Enables debugging |
| 6 | Concurrency/locking | High | Required for multi-user |
| 7 | Solver heuristics | High | Makes solver practical |
| 8 | Cost-based optimizer | High | Enables scale |
| 9 | Language bindings | Medium | Broader adoption |
| 10 | Modules/imports | Medium | Enables large projects |

---

## Maturity by Area

| Area | Maturity | What Exists | Critical Gap |
|------|----------|-------------|--------------|
| **Query** | 70% | Chase, optimization, temporal ops | No cost-based optimization |
| **Solver** | 65% | Explicit tree, tactics framework | No heuristics, no backtracking |
| **Storage** | 75% | Append-only, versioning | No concurrency, no recovery |
| **API** | 45% | Clean Rust library | No REST, no LSP, no FFI |
| **Performance** | 40% | Fuzzing, property tests | No benchmarks, no profiling |
| **Debugging** | 50% | Error formatting, query plans | No logging, no debugger |
| **Errors** | 60% | Recoverable, source spans | String-only, limited context |
| **Docs** | 65% | Architecture, inline comments | No IDE support, no tutorials |