We are developing a printer that builds functional, 3-D structures by reversible assembly of a discrete set of "digital materials." This approach uses the components rather than a control system to impose the spatial and functional constraints. Printing can be performed as a parallel rather than a linear process; the printing process is reversible for re-use of the pieces or error correction at any point in the object�s life. Error detection, error-reduction, and error-tolerance during assembly allow for reliable, high-throughput printing. We are presenting development approaches to such a printing device.