For what it's worth, I do sometimes define a version of MonadReader's "local" for MonadState; it runs a State computation on a transformed State. I've heard this used often enough to wonder why it's not a standard part of MonadState.
> On Nov 20, 2019, at 1:08 PM, Jacques Carette <carette@mcmaster.ca> wrote:
>
> In the particular case of interest, I am interested in is actually b -> State a c -> (State (a,b) c), which is of course a special case of the above.
>
> Use case: a Stateful computation where a local sub-computation needs more (local) state that will be, in-time, de-allocated.
Perhaps I misunderstood your use-case, but it seems that with a local
sub-computation that needs extra state you can just:
...
st <- get
(c, (st', _)) <- runStateT local (st, extra)
put st'
...
where local :: StateT (a, b) m c.
--
Viktor.
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