Re: [Haskell-cafe] Re: [Haskell] [ANN] Safe Lazy IO in Haskell

I've posted it once or twice. newtype C m r a = C ((a -> m r) -> m r) It's a monad, regardless of whether m is one or not. If you have something like "return" and "bind", but not exactly the same, you can make "casting" functions m a -> C m r a and backwards. Jason Dusek wrote on 19.05.2009 10:23:

2009/05/18 Miguel Mitrofanov :

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On 19 May 2009, at 09:06, Ryan Ingram wrote:

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This is a common problem with trying to use do-notation; there are some cases where you can't make the object an instance of Monad. The same problem holds for Data.Set; you'd can write

setBind :: Ord b => Set a -> (a -> Set b) -> Set b setBind m f = unions (map f $ toList m)

but there is no way to use setBind for a definition of >>= You can use a continuation trick.

Trick?

-- Jason Dusek _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe