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.
   
  +
* [[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.haskell.org/hawiki/MonadsAsContainers Monads as Containers]

Revision as of 02:31, 19 March 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.