[Haskell-cafe] Re: Can we come out of a monad?

[Brandon S Allbery KF8NH]

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On 7/30/10 11:48 , Ivan Lazar Miljenovic wrote:
> Ertugrul Soeylemez <es at ertes.de> writes:
>> it's a bit hidden in Haskell, but a monad instance consists of three
>> functions:
>>
>>   fmap   :: (a -> b) -> (m a -> m b)
> 
> You don't even need fmap defined for it to be a monad, since fmap f m =
> liftM f m = m >>= (return . f)

fmap/join and return/bind are isomorphic; given either set, you can produce
the other.  The usual category-theory definition of monads uses the former;
Haskell uses the latter, because it allows operations to easily be chained
together.

- -- 
brandon s. allbery     [linux,solaris,freebsd,perl]      allbery at kf8nh.com
system administrator  [openafs,heimdal,too many hats]  allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university      KF8NH
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