Crate lemma 

Lemma Engine

Rules for man and machine

Lemma is a declarative programming language for expressing rules, data, and business logic in a way that is both human-readable and machine-executable.

Quick Start

use lemma::{Engine, SourceType};

let mut engine = Engine::new();

// Load Lemma code
engine.load(r#"
    spec example
    data price: 100
    data quantity: 5
    rule total: price * quantity
"#, SourceType::Path(std::sync::Arc::new(std::path::PathBuf::from("example.lemma")))).expect("failed to load");

// Evaluate the spec (all rules, no data values)
let now = lemma::DateTimeValue::now();
let response = engine.run(None, "example", Some(&now), std::collections::HashMap::new(), false).unwrap();

Core Concepts

Specs

A spec is a collection of data and rules. Specs can reference other Specs to build composable logic.

Data

Data are named values: numbers, text, dates, booleans, or typed units like 50 kilograms or 100.

Rules

Rules compute values based on data and other rules. They support conditional logic through “unless” clauses.

Types

Lemma has a rich type system including units (mass, length, time, money) with automatic conversions.

Re-exports

pub use deps::dependency_cache_file;

pub use deps::dependency_identifier_from_dependency_path;

pub use deps::lemma_deps_dir;

pub use deps::relative_dependency_cache_path;

pub use engine::collect_lemma_sources;

pub use engine::Context;

pub use engine::Engine;

pub use engine::Errors;

pub use engine::ResolvedRepository;

pub use error::Error;

pub use error::ErrorKind;

pub use error::RequestErrorKind;

pub use evaluation::explanation;

pub use evaluation::operations::OperationResult;

pub use evaluation::operations::VetoType;

pub use evaluation::response::DataGroup;

pub use evaluation::response::Response;

pub use evaluation::response::RuleResult;

pub use formatting::format_source;

pub use inversion::Bound;

pub use inversion::Domain;

pub use inversion::Target;

pub use limits::ResourceLimits;

pub use parsing::ast::DateTimeValue;

pub use parsing::ast::EffectiveDate;

pub use parsing::ast::LemmaRepository;

pub use parsing::ast::LemmaSpec;

pub use parsing::parse;

pub use parsing::source::SourceType;

pub use parsing::ParseResult;

pub use planning::semantics::DataPath;

pub use planning::semantics::LemmaType;

pub use planning::semantics::LiteralValue;

pub use planning::semantics::TypeSpecification;

pub use planning::semantics::ValueKind;

pub use planning::ExecutionPlan;

pub use planning::LemmaSpecSet;

pub use planning::SpecSchema;

Modules

deps

Dependency cache layout under <workdir>/.deps/, shared by CLI fetch and LSP.

engine

error

evaluation

Pure Rust evaluation engine for Lemma

formatting

Lemma source code formatting.

inversion

World-based inverse reasoning for Lemma rules

limits

parsing

planning

Planning module for Lemma specs

registry

Registry trait, types, and resolution logic for external repository references.

serialization

Serialization: Lemma values ↔ JSON.

spec_set_id

Parse spec set identifiers: a single spec set name.