Proposal: add 'state' to the MonadState class

[Bas van Dijk]

On 26 September 2011 16:25, Twan van Laarhoven <twanvl at gmail.com> wrote:
> Hello list,
>
>
> Currently the 'state' function is only defined for the State type (aka
> StateT Identity):
>
>    state :: (s -> (a, s)) -> State s a
>    state f = StateT (Identity . f)
>
> But this function makes sense for all MonadState instances. I therefore
> propose to either add it to the MonadState class:
>
>    class MonadState s m | m -> s where
>        ...
>        state :: (s -> (a,s)) -> m a
>        state f = do s <- get
>                     let (a,s') = f s
>                     set s'
>                     return a
>
> or as a stand alone function like modify. I personally prefer to add it to
> the class, since that allows for a more efficient implementation. In
> particular:
>
>    instance Monad m => MonadState s (StateT s m) where
>        ....
>        state = StateT (return . f)
>
>
> Discussion period: 2 weeks  (ends October 10th)
>
>
> Twan
>
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+1

What happend to this proposal?

Edward, could you also list yourself as maintainer of mtl and list the
repository in the cabal file[1]?

Cheers,

Bas

[1] http://www.haskell.org/cabal/users-guide/#source-repositories