Monad
From HaskellWiki
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* [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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== Monad Reference Guides == | == Monad Reference Guides == |
Revision as of 10:48, 4 September 2006
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.
1 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.
- Monads as Containers
- All About Monads
- Simple monad examples
- Of monads and space suits
- You could have invented monads
- Meet Bob The Monadic Lover
2 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.