Where prelude alternatives/ classes and types to get values?

[Neil Mitchell]

Hi

> I could imagine a class
>
> class ModifyIO m c where
> modify :: IORef a -> ( a -> a ) -> m c

m would have to be IO, c would be a bit pointless - so IO () is a
better return type.

You can then Hoogle for it: IORef a -> (a -> a) -> IO ()

http://haskell.org/hoogle/?q=IORef%20a%20-%3E%20(a%20-%3E%20a)%20-%3E%20IO%20()


 ... = do (New count) <- modify ioCounterRef (+1)

 = do newcount <- modifyIORef ioCounterRef (+1)

It already exists :)

Thanks

Neil