[Haskell-cafe] Help mixing pure and IO code

Felipe Lessa felipe.lessa at gmail.com
Sun Nov 29 11:07:33 EST 2009

On Sun, Nov 29, 2009 at 03:11:23PM +0100, papa.eric at free.fr wrote:
> However, I wonder how to do it reusing the "pure" versions,
> runGame and Strategy?

There's a nice approach to this problem which is described and
implemented in the MonadPrompt package[1].  Basically you have

    prompt :: MonadPrompt p m => p a -> m a

which allows you to interact with the outside world.  The beauty
here is that the interection is generic, you may write a pure
simulator (like yours), an IO-heavy game (like what you're
trying) and possibly more, like unit tests and property checks.


[1] http://hackage.haskell.org/package/MonadPrompt


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