Commerce as a formal system.

import { order } from "@warp-lang/commerce-types";

// Build a valid order: buyer, seller, a priced item, paid + fulfilled.
const built = order()
  .from("buyer_1")
  .to("seller_1")
  .item({ sku: "TSHIRT-RED-M", price: { amount: 200, currency: "MAD" } })
  .paid()
  .fulfilled()
  .build(); // Result<AuditedOrder> = { ok: true, value } | { ok: false, error }

if (built.ok) {
  const violations = built.value.audit(); // []  — the headline check, clean
}

// A buggy order — two currencies in one order — is surfaced as a Result,
// not coerced into a broken object.
const mixed = order()
  .from("buyer_1").to("seller_1")
  .value({ amount: 200, currency: "MAD" })
  .value({ amount: 30, currency: "EUR" })
  .build();

if (mixed.ok === false) {
  mixed.error; // "Order mixes currencies (MAD, EUR)… (Invariant 1: Value Conservation)"
}

from warp_commerce_types import (
    Money, party_id, new_commitment, transition_commitment, add,
)

# Money always carries its currency — Decimal alone is not valid Money.
price    = Money(amount=200, currency="MAD")
shipping = Money(amount=30,  currency="MAD")
total    = add(price, shipping)               # Money(amount=230, currency="MAD")

# A commitment moves through a validated state machine.
order = new_commitment(party_id("buyer"), party_id("seller"))

# Valid: Draft -> Proposed. The result carries ok / value / error.
proposed = transition_commitment(order, {"type": "Proposed"}, party_id("buyer"))
if proposed.ok:
    print("state:", proposed.value.state.type)    # "Proposed"

# Invalid: Draft -> Fulfilled is not in the table. Caught, not raised.
bad = transition_commitment(order, {"type": "Fulfilled"}, party_id("buyer"))
if not bad.ok:
    print("rejected:", bad.error)                 # explains the violation