Advances in parallel computing have made it clear that the ability to express computations in a machine-independent manner and the ability to handle dynamic and irregular computations are two necessary features of future programming systems. In this paper, we describe the nested data-parallel model of programming, which has both these capabilities. We present an intermediate-level language called VCODE embodying the properties of the model. We discuss several representative irregular problems and show both their expression in the model and their performance on shared-memory multiprocessors. We also briefly discuss the compiler techniques necessary for achieving good performance on MIMD machines with this programming model.