[Haskell-beginners] About monad

[Trung Quang Nguyen]

Hi David,

Yours is more precise. f should output (ValueConstructor value) instead of
(Monad value) :)

--Trung




2012/12/20 David McBride <toad3k at gmail.com>

> 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 <trungnq97 at gmail.com>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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>>
>>
>


-- 
*Trung Nguyen*
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