Many tree and dag pipe notations have been proposed. Marc's was one of the first. I devised one myself, but didn't like it enough to publish it even as a TM. A recent one is Spinellis's dgsh. More elaborate networks with feedback loops evolve for power-series computation. The idea of implementing cellular automata as arrays of processes with nearest neighbors connected by pipes was suggested early on, but I've never seen such an arrangement implemented--it would be hideously slow. I once wrote a general plumber that worked from a connection list: connect fd m in process A to fd n in process B. The main challenge was to find an order of hooking things up so that the number of live file descriptors in the plumber didn't exceed the system limit. Doug