  This manuscript gives a category-theoretic foundation to the composition of
State Threads as a Foundation for Monadic Dataflow Parallelism. It serves as a
supplementary formalization of the concepts introduced in the Article "STCLang:
State Thread Composition as a Foundation for Monadic Dataflow Parallelism", as
published in Proceedings of the 12th ACM SIGPLAN International Symposium on
Haskell (Haskell'19).
