[Haskell-cafe] How to implement instance of MonadBaseControl IO

[Chris Wong]

On Wed, Aug 22, 2012 at 7:16 PM, yi huang <yi.codeplayer at gmail.com> wrote:
> I have a `newtype Yun a = Yun { unYun :: ReaderT YunEnv (ResourceT IO) a }`
> , and i need to define an instance of `MonadBaseControl IO` for it.
> Newtype instance deriving don't work here. I guess the answer is simple, i
> just can't figure it out, hope anybody can lightening me.

I had the same problem some time ago. In my case it's StateT instead
of ReaderT, but it's the same idea. The tough part is getting around
the crazy CPS -- it's supposed to help with performance, but at the
cost of usability.

Anyway, here's my implementation:
https://github.com/lfairy/haskol/blob/master/Web/KoL/Core.hs#L58

Michael Snoyman has written a tutorial as well:
http://www.yesodweb.com/book/monad-control
I'd recommend printing it out and going over it slowly -- it can get
pretty dense at times.

Chris

> Best regards.
> Yihuang.
>
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