On Wed, Feb 25, 2009 at 10:05 PM, Henning Thielemann
<[email protected]> wrote:

>> I guess it is related. It is possible that I do not know how to use
>> 'transformers' properly.
>> Specifically:
>>
>> http://hackage.haskell.org/packages/archive/data-accessor/0.1.4/doc/html/Data-Accessor.html
>>
>> getA :: MonadState r m => Accessor r a -> m a
>>
>> http://hackage.haskell.org/packages/archive/data-accessor/0.2.0.2/doc/html/Data-Accessor.html
>>
>> getA :: Monad m => Accessor r a -> StateT r m a
>>
>> I'd rather not rewrite the monads to the StateT form...
>> I'm now writing a compatibility layer, but I feel it would be better if
>> the data-accessor package supported the old interface.
>
> In 'transformers', State r = StateT r Identity, thus there is no need for
> the MonadState class, which is not Haskell 98.

Unfortunately this forces to put the StateT on top of the transformer
stack, which is
not always practical.

> I could reactivate the old
> MonadState module and publish it as MonadState.MTL in a separate package.

I'd like that!

The classes are in monads-fd; so I guess the name could derive from that.

Many thanks!
-- JP

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