Yes, I remember seeing a talk by Edward Kmett (at some Scala user group I think) where he said lenses allowed you to focus on a substate in the state monad.
Paul
On Tue Jan 27 2015 at 11:21:35 PM PkmX <
pkmx.tw@gmail.com> wrote:
Isn't this exactly what the `zoom` function does from `Control.Lens.Zoom`?
> flip execState (1, 1) $ zoom _1 $ modify succ
(2, 1)
On Wed, Jan 28, 2015 at 6:14 AM, Christopher Done <chrisdone@gmail.com> wrote:
> runSubStateT :: Monad m
> => (s -> s') -> (s' -> s) -> StateT s' m a -> StateT s m a
> runSubStateT to from m =
> StateT (\s ->
> liftM (\(a,s') -> (a,from s'))
> (runStateT m (to s)))
>
> Anyone ever needed something like this? Does it already exist in some
> form in the standard libraries?
>
> Ciao
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--
Chih-Mao Chen (PkmX)
System Software Laboratory
Department of Computer Science
National Chiao Tung University
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