Difference between revisions of "Monad"

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m (Add a link to sigfpe's monad tutorial.)
m (added link to Meet Bob The Monadic Lover)
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* [http://www.loria.fr/~kow/monads/index.html Of monads and space suits]
 
* [http://www.loria.fr/~kow/monads/index.html Of monads and space suits]
 
* [http://sigfpe.blogspot.com/2006/08/you-could-have-invented-monads-and.html You could have invented monads]
 
* [http://sigfpe.blogspot.com/2006/08/you-could-have-invented-monads-and.html You could have invented monads]
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* [[Meet Bob The Monadic Lover]]
   
 
== Monad Reference Guides ==
 
== Monad Reference Guides ==

Revision as of 10:48, 4 September 2006

Monad class (base)
import Control.Monad

The Monad class is defined like this:

class Monad m where
  (>>=) :: m a -> (a -> m b) -> m b
  (>>) :: m a -> m b -> m b
  return :: a -> m a
  fail :: String -> m a

All instances of Monad should obey:

return a >>= k  =  k a
m >>= return  =  m
m >>= (\x -> k x >>= h)  =  (m >>= k) >>= h

Any Monad can be made a Functor by defining

fmap ab ma = ma >>= (return . ab)

However, the Functor class is not a superclass of the Monad class. See Functor hierarchy proposal.

Monad Tutorials

Monads are known for being deeply confusing to lots of people, so there are plenty of tutorials specifically related to monads. Each takes a different approach to Monads, and hopefully everyone will find something useful.

Monad Reference Guides

An explanation of the basic Monad functions, with examples, can be found in the reference guide A tour of the Haskell Monad functions, by Henk-Jan van Tuyl.