Re: [Haskell-beginners] About monad

Hi David, Yours is more precise. f should output (ValueConstructor value) instead of (Monad value) :) --Trung 2012/12/20 David McBride

The way I like to reason about these things Prelude> :t (>>=)

(>>=) :: Monad m => m a -> (a -> m b) -> m b

Since the Monad m in this definition is Maybe, I'll just substitute it in like so: Maybe a -> (a -> Maybe b) -> Maybe b

Then you notice that f is not (a -> b), it is (a -> Maybe b).

On Thu, Dec 20, 2012 at 9:07 AM, Trung Quang Nguyen wrote:

...

Hi all,

I saw this

1. instance Monad Maybe where 2. return x = Just x 3. Nothing >>= f = Nothing 4. Just x >>= f = f x 5. fail _ = Nothing

I am wondering about the implementation of function (>>=). Why don't it be *Just x >>= f = Just (f x)*?

Any body knows about this?

--Trung

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