The generic model for stateful computation (S -> S x R) provides a convenient mechanism of threading stateful computation results since the functor λR . S -> S x R is monadic. But what happens if we want to thread state itself? Well, the mapping λS. S -> S x R is not even functorial! But it turns out it can become so with a bit of trickery. This snippet demonstrates a way to lift, project or inject stateful computations into ambient state monads.
8 people like thisPosted: 5 years ago by Eirik Tsarpalis