Construction and analysis of distributed systems is difficult. Multiparty session types (MPST) constitute a method to make it easier. In practice, the premier approach to apply the MPST method in combination with mainstream programming languages has been based on API generation. In this paper (pearl), we revisit and revise this approach.

Regarding our “revisitation”, using Scala 3, we present the existing API generation approach, which is based on deterministic finite automata (DFA), in terms of both the existing states-as-classes encoding of DFAs as APIs, and a new states-as-type-parameters encoding; the latter leverages match types in Scala 3. Regarding our “revision”, also using Scala 3, we present a new API generation approach that is based on sets of pomsets instead of DFAs; it crucially leverages match types, too. Through this fresh perspective, which can avoid two forms of combinatorial explosion that the DFA-based approach suffers from, we show how to effectively support an important feature—concurrent subprotocols—for the first time; it is incorporated in a new tool, which we present as well.