;How can I make [transactions] not an external reference in my deftype Portfolio?

(defrecord Tx [date symbol type qty price])
(defrecord Tick [date symbol price])

(defprotocol IPortfolio
    (add [this tx] "Add transaction to portfolio")
    (del [this index] "Remove transaction from portfolio")
    (size [this] "Number of transactions")
    (view [this] "Return all transactions")
    )


;transactions - ref to vector

(deftype Portfolio [transactions]
    IPortfolio
    (add [this transaction]
        (dosync (alter transactions conj transaction)))

    (del [this index]
        (dosync (commute transactions delete-element index)))

    (size [this]
        (count @transactions))

    (view [this]
        @transactions)
)