commerce-theory

Runtime Rust mirror of the CommerceTheory Lean package.

This crate turns the Lean model's proof-carrying commerce records into ordinary Rust domain types with private fields, smart constructors, executable predicates, checked arithmetic, and tests for the headline safety guarantees.

What It Models

The crate covers e-commerce and marketplace invariants across:

• foundation units, IDs, currency, money, basis points, and profit arithmetic
• catalog, inventory, pricing, orders, payments, refunds, and accounting
• marketplace listings, feeds, payouts, marketing, B2B, and wholesale credit
• dropshipping, supplier capacity, purchase orders, returns, and profit floors
• competitor pricing, merchandising, fulfillment finance, risk, and privacy
• event sourcing, event validation, replay, workflows, keyed totals, and ranking

All modules are re-exported from the library root:

use commerce_theory::*;

Design

Lean proof fields are represented as runtime validation:

• data fields are private;
• try_new constructors enforce invariants;
• simple records also provide new where there is no invariant to check;
• predicates return bool;
• arithmetic that can overflow returns Result<_, ValidationError>;
• natural-number subtraction uses saturating subtraction to match Lean Nat subtraction flooring at zero.

The crate uses u128 aliases for Lean Nat-style quantities:

pub type Money = u128;
pub type Quantity = u128;
pub type Weight = u128;
pub type Timestamp = u128;
pub type Days = u128;
pub type Id = u128;

Example

use commerce_theory::*;

fn main() -> Result<(), ValidationError> {
    let line = CartLine::try_new(Sku::new(1), 100, 40, 2, 20, 3)?;
    assert_eq!(line_gross_total(&line)?, 200);
    assert_eq!(line_net_total(&line)?, 180);

    let shipping = ShippingMethod::new(15, 500, 20);
    let items = vec![line];
    let total = order_total(&shipping, 10, 5, &items)?;

    let order = Order::try_new(
        OrderId::new(7),
        items,
        10,
        shipping,
        5,
        Currency::USD,
        OrderStatus::New,
        total,
    )?;

    assert_eq!(order.total(), total);
    Ok(())
}

Optional Serde Support

Serde derives are available behind the serde feature:

cargo test --features serde

Verification

Run the Rust checks:

cargo fmt --check
cargo test
cargo test --all-features
cargo clippy --all-targets --all-features -- -D warnings
cargo doc --all-features --no-deps

Crate Layout

• src/foundation.rs: shared IDs, units, money, currencies, validation errors
• src/catalog.rs, src/inventory.rs, src/pricing.rs, src/orders.rs
• src/accounting.rs, src/marketplace.rs, src/marketing.rs, src/b2b.rs
• src/dropshipping.rs, src/dropship_profit.rs, src/competitor_pricing.rs
• src/merchandising.rs, src/fulfillment_finance.rs, src/risk_privacy.rs
• src/event_sourcing.rs, src/event_language.rs, src/event_replay.rs
• src/post_purchase.rs, src/forecasting.rs, src/implicit_invariants.rs
• src/inventory_algorithms.rs, src/keyed_totals.rs, src/opportunity_portfolio.rs, src/opportunity_ranking.rs, src/workflow.rs
• src/summary.rs: theorem-style regression tests for the runtime mirror