Fwd: [Haskell-cafe] Re: Simple game: a monad for each player

[Limestraël]

Okay, I start to understand better...

Just, Heinrich, how would implement the mapMonad function in terms of the
operational package?
You just shown the signature.

2010/4/14 Bertram Felgenhauer <bertram.felgenhauer at googlemail.com>

> Limestraėl wrote:
> > Okay, I just understood that 'Prompt' was just a sort of view for
> 'Program'.
>
> Right.
>
> > >   runMyStackT :: MyStackT (Player m) a -> Player m a
> >
> > According to what Bertram said, "each strategy can pile its own custom
> monad
> > stack ON the (Player m) monad".
>
> Yes, and I meant what Heinrich wrote, you wrap some transformer around
> the common Player m monad.
>
> > > game :: Monad m => Player m () -> Player m () -> m ()
> > As it is written, it requires both players to run in the SAME monad.
> > And if have a network player ( e.g.* Player (StateT Handle IO)* ) and an
> AI
> > storing former opponent's moves ( e.g. *(Monad m) => Player (StateT
> [Move]
> > m)* ), then they can't be in the same monad...
>
> The idea is to pick m = IO, and then use
>
>  type NetPlayer a = StateT Handle (Player IO) a
>
> and
>
>  type AIPlayer a = StateT [Move] (Player IO) a
>
> or possibly
>
>  type AIPlayer a = StateT [Move] (Player Identity) a
>
> using the mapPlayerM (or mapMonad as suggested by Heinrich) function.
>
> You'd then provide functions like
>
>    runAIPlayer :: AIPlayer a -> Player IO a
>    runAIPlayer player = {- mapMonad (return . runIdentity) $ -}
>        evalStateT player []
>
> This gives you most of what you want: You can add custom state and the
> like to each player. You can not hope to exchange the base monad m,
> because then the 'game' function would have to know how to run both
> of those base monads simultaneously. A function like mapMonad is the
> best device you can hope for, I think.
>
> regards,
>
> Bertram
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