RealWorld -package:rebase is:exact -package:vector -package:prim-uniq package:massiv

data RealWorld
massiv Data.Massiv.Array.Mutable
RealWorld is deeply magical. It is primitive, but it is not unlifted (hence ptrArg). We never manipulate values of type RealWorld; it's only used in the type system, to parameterise State#.