Difference between revisions of "Monad"

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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.
 
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.
   
  +
* [[Monads as Containers]]
 
* [http://www.nomaware.com/monads/html/index.html All About Monads]
 
* [[Simple Monad Examples]]
 
* [[Simple Monad Examples]]
 
* [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://www.haskell.org/hawiki/MonadsAsContainers Monads as Containers]
 
* [http://www.nomaware.com/monads/html/index.html All About Monads]
 
   
 
[[Category:Standard classes]]
 
[[Category:Standard classes]]

Revision as of 08:49, 9 May 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.