[Haskell-cafe] class Ref...
gracjan at acchsh.com
Tue Jun 7 08:52:50 EDT 2005
Bulat Ziganshin wrote:
> Hello Gracjan,
> Tuesday, June 07, 2005, 2:25:50 PM, you wrote:
> class Monad m =>> Ref m r | m -> r where
> GP> newRef :: a -> m (r a)
> GP> readRef :: r a -> m a
> GP> writeRef :: r a -> a -> m ()
> may be the following will be even more interesting:
I like it very much!
> import Control.Monad
> import Data.IORef
> infixl 0 =:, +=, -=, =::, <<=
> ref = newIORef
> val = readIORef
> a=:b = writeIORef a b
Pretty shame := is already reserver :(. There is something alike
Graphics.Rendering.OpenGL.GL.StateVar. The use $= for assignment.
Generalizing "variables" (in respect to some monad) seems to be often
reinvented idea :)
As I see this could be generalized to all Ref-like constructs
> a+=b = modifyIORef a (\a-> a+b)
> a-=b = modifyIORef a (\a-> a-b)
> a=::b = ((a=:).b) =<< val a
Is this convoluted modify? Why doesn't it use modifyIORef? Or am I wrong?
> for :: [a] -> (a -> IO b) -> IO ()
> for = flip mapM_
foreach = flip mapM
foreach_ = flip mapM_
> newList = ref 
> list <<= x = list =:: (++[x])
Is this append?
> push list x = list =:: (x:)
> pop list = do x:xs<-val list; list=:xs; return x
> main = do
> sum <- ref 0
> lasti <- ref undefined
> for [1..5] $ \i -> do
> sum += i
> lasti =: i
> sum =:: (\sum-> 2*sum+1)
> print =<< val sum
> print =<< val lasti
> xs <- newList
> for [1..3] (push xs)
> xs <<= 10
> xs <<= 20
> print =<< val xs
Haskell as ultimate imperative language :)
> I use this module to simplify working with references in my program.
> The first inteface can be used for IORef/STRef/MVar/TVar and second
> for lists and Chan
Then we should create classes for those interfaces.
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