My understanding is he is using ideas from propagators and other places to make a performant logic programming framework in Haskell.
"a common knowledge base, the "blackboard", is iteratively updated by a diverse group of specialist knowledge sources, starting with a problem specification and ending with a solution. Each knowledge source updates the blackboard with a partial solution when its internal constraints match the blackboard state. In this way, the specialists work together to solve the problem"
I can't see the term Blackboard used in the paper. Probably irrelevant but just an observation.
Unlike what is explained OP, the computation is one way.
Edit: found Radul's thesis: https://dspace.mit.edu/bitstream/handle/1721.1/54635/6035432...