PersistentRelModule

allows instructions to refer to the type of program in which they are embedded. That is, K will be instantiated into FreeK[F, ?], where F[_[_], _] is a superset of this instruction set (i.e. there is an injection from Lang to F).

Some states need to store programs or program-producing functions. This type parameter allows the state to talk about the type of programs. It will be instantiated into FreeK[F, ?], where F[_[_], _] is a superset of the instruction set Lang (i.e. there is an injection from Lang to F).