state package:monoid-subclasses

This module defines the monoid transformer data type Stateful.

> let s = setState [4] $ pure "data" :: Stateful [Int] String
> s
Stateful ("data",[4])
> factors s
[Stateful ("d",[]),Stateful ("a",[]),Stateful ("t",[]),Stateful ("a",[]),Stateful ("",[4])]

Stateful a b is a wrapper around the Monoid b that carries the state a along. The state type a must be a monoid as well if Stateful is to be of any use. In the FactorialMonoid and TextualMonoid class instances, the monoid b has the priority and the state a is left for the end.