[Haskell-cafe] haskell2010 and state question.

[Henning Thielemann]

Henk-Jan van Tuyl schrieb:
> On Wed, 08 Dec 2010 10:03:40 +0100, Magicloud Magiclouds
> <magicloud.magiclouds at gmail.com> wrote:
> 
>> Hi,
>>   Formerly, I had IORef and some state monad to do the task of keeping
>> states.
>>   Now in haskell 2010, I cannot find anything about it. Do I have to
>> use ghc base package for this function?
> 
> These are not standard Haskell '98 or Haskell 2010. You can find IORef
> in the base package; the state monad is in both the mtl and the
> transformers package (mtl is deprecated). The state monad uses the
> multi-parameter type class extension and is therefore not in standard
> Haskell '98 or Haskell 2010 code.

Since mtl is split into transformers (Haskell 98 compatible code) and
the multi-parameter type classes in mtl-2/monad-fd, you can use the
State monad in Haskell 98 and Haskell 2010 code.