Monads

[Ken Shan]

Mark Carroll <mark at chaos.x-philes.com> wrote in article <Pine.LNX.4.58.0312311841030.15190 at niagara.mtbc.internal> in gmane.comp.lang.haskell.cafe:
> Omitting the typeclass bit, I'm trying to write something like
> (s1 -> s2) -> StateT s1 m () -> StateT s2 m a -> StateT s1 m a
> 
> That is, it sequences two StateT computations, providing a way to
> translate from the first's state to the second to keep the chain
> going.

Don't you need a (s2 -> s1) function as well, to translate the final
state back into StateT s1?

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