Rust Examples

This page provides an overview of the Rust example projects included with Scallop.

Location

All Rust examples are located in the repository at:

scallop/examples/rust/

Available Examples

The following 6 example projects demonstrate different aspects of the Scallop Rust API:

1. basic_datalog - Getting Started

What it demonstrates:

• Creating an IntegrateContext
• Adding Scallop programs
• Running queries
• Iterating over results

Difficulty: ⭐ Beginner

Run:

cd examples/rust/basic_datalog
cargo run

2. probabilistic_reasoning - Probabilistic Queries

What it demonstrates:

• Using MinMaxProbProvenance
• Adding facts with probabilities
• Interpreting confidence scores
• Probabilistic transitive closure

Difficulty: ⭐⭐ Intermediate

Run:

cd examples/rust/probabilistic_reasoning
cargo run

3. foreign_functions - Custom Rust Functions

What it demonstrates:

• Implementing the ForeignFunction trait
• String manipulation functions
• Numeric operations
• Registering functions with IntegrateContext

Difficulty: ⭐⭐ Intermediate

Run:

cd examples/rust/foreign_functions
cargo run

4. foreign_predicates - Fact Generators

What it demonstrates:

• Implementing the ForeignPredicate trait
• Binding patterns (bf, ff)
• Generating multiple results
• External data integration

Difficulty: ⭐⭐⭐ Advanced

Run:

cd examples/rust/foreign_predicates
cargo run

5. incremental_evaluation - Dynamic Updates

What it demonstrates:

• Creating incremental contexts
• Adding facts incrementally
• Re-running after updates
• Efficient incremental computation

Difficulty: ⭐⭐ Intermediate

Run:

cd examples/rust/incremental_evaluation
cargo run

6. complex_reasoning - Advanced Provenance

What it demonstrates:

• TopKProofsProvenance for proof tracking
• Extracting derivation proofs
• Weighted Model Counting
• Complex reasoning patterns

Difficulty: ⭐⭐⭐ Advanced

Run:

cd examples/rust/complex_reasoning
cargo run

Prerequisites

Nightly Rust Required:

rustup default nightly

Scallop requires nightly Rust due to unstable features:

• min_specialization
• extract_if
• hash_extract_if
• proc_macro_span

Building All Examples

From the examples/rust/ directory:

for example in basic_datalog probabilistic_reasoning foreign_functions foreign_predicates incremental_evaluation complex_reasoning; do
    echo "Building $example..."
    cd $example && cargo build && cd ..
done

Running All Examples

From the examples/rust/ directory:

for example in basic_datalog probabilistic_reasoning foreign_functions foreign_predicates incremental_evaluation complex_reasoning; do
    echo "=== Running $example ==="
    cd $example && cargo run && cd ..
    echo ""
done

Project Structure

Each example follows this structure:

example_name/
├── Cargo.toml          # Dependencies and project config
├── src/
│   └── main.rs         # Example code with comments
└── README.md           # Example-specific documentation

Common Patterns

Creating a Context

#![allow(unused)]
fn main() {
use scallop_core::integrate::*;
use scallop_core::runtime::provenance::discrete::unit::UnitProvenance;
use scallop_core::runtime::env::RcFamily;

let prov = UnitProvenance::default();
let mut ctx = IntegrateContext::<_, RcFamily>::new(prov);
}

Adding a Program

#![allow(unused)]
fn main() {
ctx.add_program(r#"
    rel edge = {(0, 1), (1, 2)}
    rel path(a, b) = edge(a, b)
    query path
"#)?;
}

Running and Querying

#![allow(unused)]
fn main() {
ctx.run()?;

let results = ctx.computed_relation_ref("path")?;
for elem in results.iter() {
    println!("{:?}", elem.tuple);
}
}

Troubleshooting

Nightly Rust Error

Error:

error[E0658]: use of unstable library feature 'min_specialization'

Solution:

rustup default nightly

Missing scallop-core Dependency

Error:

error: failed to load manifest for dependency `scallop-core`

Solution: Update Cargo.toml with correct path:

[dependencies]
scallop-core = { path = "../../../core" }

Type Inference Issues

If you encounter type inference errors with generics, specify types explicitly:

#![allow(unused)]
fn main() {
// Instead of:
let mut ctx = IntegrateContext::new(prov);

// Use:
let mut ctx = IntegrateContext::<_, RcFamily>::new(prov);
}

Next Steps

After exploring the examples:

• Getting Started Guide - Introduction to Scallop Rust API
• IntegrateContext API - Complete API reference
• Foreign Functions - Custom Rust functions
• Foreign Predicates - Fact generators
• Provenance Types - Reasoning semantics

Contributing

Have an example you’d like to add? Contributions welcome!

1. Create a new directory under examples/rust/
2. Follow the standard project structure
3. Add entry to this documentation
4. Ensure it builds with cargo build
5. Submit a pull request

Resources

• Scallop Repository - Main repository
• Scallop Language Guide - Scallop language reference
• Python API Examples - Python bindings examples