Effectful Mealy Machines: Bisimulation and Trace

We introduce effectful Mealy machines - a general notion of Mealy machine with global effects - and give them semantics in terms of both effectful bisimilarity and traces. Bisimilarity of effectful Mealy machines is characterised syntactically in terms of uniform feedback. Traces of effectful Mealy machines are given a novel semantic coinductive universe, in terms of effectful streams. We prove that effectful streams generalise a standard notion of causal process, capturing existing flavours of Mealy machine, bisimilarity, and trace.