Mass. Gen. Laws ch. 109, § 34

Except as provided in sections thirty-one to thirty-eight, inclusive, upon withdrawal any withdrawing partner is entitled to receive any distribution to which he is entitled under the partnership agreement and, if not otherwise provided in the agreement, he is entitled to receive, within a reasonable time after withdrawal, the fair value of his interest in the limited partnership as of the date of withdrawal based upon his right to share in distributions from the limited partnership.