test.ml

type instruction =
  | Order of {id: int; price: float; size: int}
  | Cancel of {id: int}
  | Cancel_replace of {id: int; new_price: float; new_size: int}

let filter_by_oid instructions oid =
  List.filter (function
      | Order o -> o.id = oid
      | Cancel c -> c.id = oid
      | Cancel_replace cr -> cr.id = oid)
    instructions