Re: [Haskell-cafe] global variables

You can also use mutable variables (MVars) found in Control.Concurrent.MVar http://haskell.org/ghc/docs/latest/html/libraries/base/Control-Concurrent-MV... They might work depending on your implementation. The reading and writing of MVars returns IO actions. On 5/17/07, Dougal Stanton wrote:

On 17/05/07, Eric wrote:

...

H|i,

Does anyone know of a simple and straightforward way to use global variables in Haskell?

You can pass around an environment with the State or Reader monads (read/write and read-only respectively). If you want to do IO with the data you'll probably need the transformer equivalents: StateT or ReaderT.

I think there are some hackish ways of making IO variables but I don't know how that's done. I'd imagine it's frowned on from a stylistic point of view, too...

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