Module `Algostream_order_management.Order_state`

Explicit state-machine helpers on top of Algostream_domain_orders.Order.order_status.

The Domain.Order module already has a 7-state status enum (Pending / Open / Partially_filled / Filled / Cancelled / Rejected / Expired) but no explicit transition table or terminal-state predicates. This module fills that gap as pure functions — transition returns the new status for the caller to apply via Order.update_status, so we do not inject a wall-clock read into our event-time-deterministic layers.

module Order = Algostream_domain_orders.Order

type status = Order.order_status

val is_terminal : status -> bool

val is_active : status -> bool

val status_name : status -> string

type transition_error =

| Invalid_transition of {
1. from_ : string;
2. to_ : string;
}
| Terminal_state of string

val can_transition : from_:status -> to_:status -> bool

Legal transitions only.

Pending → Open | Cancelled | Rejected
Open → Partially_filled | Filled | Cancelled | Rejected | Expired
Partially_filled → Partially_filled (more fills) | Filled | Cancelled | Expired
Terminal states (Filled, Cancelled, Rejected, Expired) → none

val transition : 
  Order.order ->
  to_:status ->
  (status, transition_error) Stdlib.result

Returns Ok new_status if the transition is valid; the caller applies it via Order.update_status. Returns Error without mutating.