## Chase-rs

An implementation of the chase algorithm in Rust for reasoning engines.

### Overview

The chase algorithm is a technique in context of database theory and knowledge representation used for:

- Query answering under tuple-generating dependencies (TGDs)
- Computing universal models
- Datalog with existential rules

This implementation provides a restricted-chase style materialization with active-trigger checks.
The default entrypoints use a `10_000` step safeguard and report incomplete results with
`terminated == false` if that limit is reached.

### Features

- **Core Data Types**: Terms, Atoms, Rules, and Instances
- **Existential Quantification**: Automatic generation of labeled nulls
- **Restricted Chase Style**: Active-trigger checks for existential rules
- **Configurable Step Limit**: `chase_with_config` exposes the step bound
- **Fluent API**: `RuleBuilder` for readable rule construction
- **Interactive Frontends**: REPL, script runner, and a local GUI
- **Zero Dependencies**: Pure Rust with no external runtime dependencies

See [ROADMAP.md](ROADMAP.md) for the list of implemented and planned features.

> [!IMPORTANT]
> This project is still in early development, so bugs and breaking changes are expected.
> Please use the [issues page](https://code.obsidian.systems/habedi-work/chase-rs/issues) to report bugs or request features.

---

### Quickstart

#### Example

```rust
use chase_rs::{chase, Atom, Instance, Term};
use chase_rs::chase::rule::RuleBuilder;

// Create initial facts
let instance: Instance = vec![
    Atom::new("Parent", vec![Term::constant("alice"), Term::constant("bob")]),
    Atom::new("Parent", vec![Term::constant("bob"), Term::constant("carol")]),
].into_iter().collect();

// Define rules
// Parent(X, Y) -> Ancestor(X, Y)
let rule1 = RuleBuilder::new()
    .when("Parent", vec![Term::var("X"), Term::var("Y")])
    .then("Ancestor", vec![Term::var("X"), Term::var("Y")])
    .build();

// Ancestor(X, Y), Parent(Y, Z) -> Ancestor(X, Z)
let rule2 = RuleBuilder::new()
    .when("Ancestor", vec![Term::var("X"), Term::var("Y")])
    .when("Parent", vec![Term::var("Y"), Term::var("Z")])
    .then("Ancestor", vec![Term::var("X"), Term::var("Z")])
    .build();

// Run the chase
let result = chase(instance, &[rule1, rule2]);

assert!(result.terminated);
println!("Derived {} facts", result.instance.len());
```

Use `chase_with_config` to change the default step bound:

```rust
use chase_rs::{Atom, ChaseConfig, Instance, Term, chase_with_config};
use chase_rs::chase::rule::RuleBuilder;

let instance: Instance = vec![Atom::new("P", vec![Term::constant("a")])]
    .into_iter()
    .collect();
let rule = RuleBuilder::new()
    .when("P", vec![Term::var("X")])
    .then("Q", vec![Term::var("X")])
    .build();

let result = chase_with_config(
    instance,
    &[rule],
    ChaseConfig { max_steps: 100 },
);

assert!(result.terminated);
```

#### Existential Rules

Rules with head-only variables (existential quantification) automatically generate fresh labeled nulls:

```rust
// Every person has an SSN: Person(X) -> HasSSN(X, Y)
let rule = RuleBuilder::new()
    .when("Person", vec![Term::var("X")])
    .then("HasSSN", vec![Term::var("X"), Term::var("Y")]) // Y is existential
    .build();
```

#### Frontends

The binary now supports three entrypoints:

```bash
# Start the interactive REPL
cargo run -- repl

# Start the local GUI at http://127.0.0.1:7878
cargo run -- gui

# Run a script file
cargo run -- script examples/scripts/ancestor.chase
```

The REPL and GUI share a minimal command language:

```text
fact Parent(alice, bob).
rule Parent(?X, ?Y) -> Ancestor(?X, ?Y).
run.
query Ancestor(?X, ?Y)?
explain Ancestor(alice, carol)?
show facts
show rules
reset
help
```

Rules:

- facts and rules end with `.`
- queries end with `?`
- `explain ... ?` shows one derivation tree per matching answer
- variables are prefixed with `?`
- quoted constants are supported, for example `"alice smith"`

#### Useful Commands

```bash
# Install dependencies
nix develop -c make install-deps

# Run all tests
make test

# Run linter checks
make lint

# Run with optimizations
make build

# Run CLI
make run
```

---

### License

This project is licensed under [BSD-3](LICENSE).