effectful-st (hackage): An ST-style alternative to the Prim effect in effectful that allows safely running scoped state transformations without IOE.  The Prim effect allows the use of PrimMonad on Eff without allowing arbitrary IO. However, there is no safe way to run the effect without introducing the IOE effect because Prim has no way of delimiting the scope of the mutation to runPrim. In other words, Prim is effectively acting merely as a restricted form of IOE that only allows PrimMonad.  STE from this package on the other hand borrows the quantification trick from Control.Monad.ST to provide a safe way to run the effect purely.
Keywords: effectful|library