CODEWITHSUNDEEP
haskellmonads
cammil
cammil

Reputation: 9909

Should bind result in a Monad?

The following is an example from a Haskell tutorial

instance Monad Maybe where  
    return x = Just x  
    Nothing >>= f = Nothing  
    Just x >>= f  = f x  
    fail _ = Nothing

However, I am confused by the Just x... line. Should the result not be a monad? I would expect the line to be

Just x >>= f = Just (f x)

Upvotes: 4

Views: 93

Answers (1)

Hackerman
Hackerman

Reputation: 153

Yes! You're right about the result being a monad, but remember the type of the >>= operator: m a -> (a -> m b) -> m b. Then, we guess that f has type a -> m b, so applying f to x returns a monad as a result.

Upvotes: 9

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