*fmap*http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.htm...
::
Functor f => (a -> b) -> f a -> f
bhttp://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.htm...
fmap f (Just a) = Just (f a)
We wrap Just around (f a) because f return a value with type b instead
(Just b).
But in
(*>>=*)http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.htm...
::
Monad m => m a -> (a -> m b) -> m
bhttp://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.htm...
Just x >>= f = f x
We don't need to wrap Just around (f a) because f return (Just b).
--Trung
2012/12/20 Miguel Negrao
A 20/12/2012, às 14:07, Trung Quang Nguyen escreveu:
Hi all,
I saw this
• instance Monad Maybe where • return x = Just x • Nothing >>= f = Nothing • Just x >>= f = f x • 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?
That would be the implementation of fmap for Maybe:
instance Functor Maybe where fmap _ Nothing = Nothing fmap f (Just a) = Just (f a)
so, different behavior.
best, Miguel _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners
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