[Haskell-beginners] IO vars & ACID

[Corentin Dupont]

To give you more context, I have a soft using ACID state to store and
retrieve values.
For example I have a function like that:

newPlayer :: PlayerName -> IO ()
newPlayer name = update $ AddPlayer name

It seems that ACID uses a global state or a file to store the events... I'd
like to suppress the ACID state for the moment, how should I do?
Change all the* IO () *types to *StateT Game IO ()*?
Indead the ACID state is started with:
c <- localStartSystemState (Proxy :: Proxy Game)

Best,
C

On Wed, Aug 29, 2012 at 12:00 PM, Corentin Dupont <corentin.dupont at gmail.com
> wrote:

> Thanks Eugene and Ozgur.
> I also looked on the side of IORef, but it doesn't looked to be a good
> solution since we have to use unsafePerformIO.
>
> I have a big program to modify, and I want to pass some new data to
> existing functions of type IO(). I'd like to avoid changing all the
> function's types down the chain... What is the best way to do that?
>
>
>
>
> On Wed, Aug 29, 2012 at 11:43 AM, Ozgur Akgun <ozgurakgun at gmail.com>wrote:
>
>> On 29 August 2012 10:21, Corentin Dupont <corentin.dupont at gmail.com>wrote:
>>
>>> *f,g :: IO ()
>>> f = withFile "toto" WriteMode (flip hPutStr "42")
>>> g = withFile "toto" ReadMode hGetLine >>= (\s -> putStrLn $ "Answer:" ++
>>> s)
>>> main = f >> g*
>>>
>>> Is it possible to do the same without files (the types must remain IO())?
>>>
>>
>> One can use an IORef to get a similar effect.
>>
>> import Data.IORef
>> import System.IO.Unsafe
>>
>> {-# NOINLINE toto #-}
>> toto :: IORef String
>> toto = unsafePerformIO (newIORef "")
>>
>> f,g :: IO ()
>> f = writeIORef toto "42"
>> g = readIORef toto >>= (\s -> putStrLn $ "Answer:" ++ s)
>>
>> main = f >> g
>>
>> HTH,
>> Ozgur
>>
>
>
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