arXiv:2611.06188v1 Announce Type: new Abstract: Progressive Visual Analytics (PVA) systems have demonstrated the effectiveness of time-bounded, incremental computation for exploring large-scale data. However, our survey reveals that existing PVA implementations are often difficult to reuse and extend, as their progressive behaviors are typically realized through ad hoc, hard-coded mechanisms distributed across servers and clients. To address this limitation, we present ProGram, a grammar for progressive computation pipelines. Informed by a comprehensive analysis of prior concepts and design practices in existing PVA systems, ProGram is designed to support core progressive features while reducing implementation burden. Furthermore, we extend the design space by introducing novel mechanisms, such as lockstepping, forking, and temporary prioritization, to better support diverse usage scenarios. Finally, we demonstrate the expressiveness and coverage of ProGram by reproducing and extending existing progressive visualization systems, presenting a gallery of progressive computation pipelines, and discussing the grammar coverage.