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Event

Syntax

event <Name> {
  <fieldName>: <TypeName>
  ...
}

Events represent facts that happened. They are immutable value objects produced by decide clauses and applied by evolve clauses.

Rules

  • Events are never constructed directly by application code.
  • Each field must reference a declared type.
  • Event names should use past tense (e.g., CartOpened, ItemAdded).

Schema Evolution (Planned)

event CartOpened @v1 {
  cartId: CartId
  customerId: CustomerId
}


event CartOpened @v2 {
  cartId: CartId
  customerId: CustomerId
  openedAt: Timestamp
  channel: Channel
}


upcast CartOpened @v1 -> @v2 {
  openedAt = epoch
  channel  = Web
}

Version annotations use @v followed by an integer. The compiler verifies transitive completeness of upcast chains.