Re: [Haskell-cafe] Can we come out of a monad?

On Mon, Aug 9, 2010 at 1:19 PM, John Lato wrote:

I don't find purify2 particularly helpful because I almost never want to break out of any arbitrary monad; I want to be able to break out of a specific monad without knowing which monad it is, that is:

purify3 :: Monad m => m a -> a purify3 = undefined  --the only possible definition...

However, I just realized that something else is almost as good:

evalCont :: Cont r a -> r evalCont k = runCont k id

Except, of course, you want the signature evalCont :: Cont r a -> a Which is not possible. But I am not sure where all this discussion is coming from, Maybe and (r ->) cannot be broken out of. Isn't that example enough? Luke