tor 2003-08-21 klockan 22.26 skrev Jon Cast:

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Yes. Many complicated proposals have been made, but there's a straightforward, general mechanism:

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addMaybe :: Num alpha => Maybe alpha -> Maybe alpha -> Maybe alpha addMaybe a b = a >>= \x -> b >>= \y -> return (x + y)

or

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addMaybe a b = do x <- a y <- b return (x + y)

or

addMaybe = Monad.liftM2 (+)

I personally use those monadic lifting functions a lot. Monad.sequence combined with list comprehension is another favorite.

So do I. But that style doesn't work as well with functions that are already in the monad. So, I mentioned the more general style. Jon Cast