base.flows.ActorImpl[S:imm,mut,read,E:imm,mut,read,R:imm,mut,read]

read #(downstream: mut base.flows._ActorSink[imm R], state: S, e: E): imm base.flows.ActorRes,
read #(downstream: mut base.flows._ActorSink[imm R], state: S, e: E): imm base.flows.ActorRes,