Re: [Haskell-beginners] Global variables

On Thu, Jun 30, 2011 at 8:21 AM, Ertugrul Soeylemez wrote:

Christopher Done wrote:

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I tend to use Control.Monad.Reader for stateful stuff like this. It is found in the mtl package http://hackage.haskell.org/package/mtl-2.0.1.0

How would you use reader for a counter?

Reader is a good choice for an interthread counter:

   MonadIO m => ReaderT (TVar Int) m

I think, then people are talking about global variables in Haskell, what they really want is such a thing.

Greets, Ertugrul

Though in this case, you can go with the cheaper IORef, since (presumably) the only operation is going to be incrementing the counter. Just be sure to use atomicModifyIORef[1]. Michael [1] http://hackage.haskell.org/packages/archive/base/4.3.1.0/doc/html/Data-IORef...