Difference between revisions of "Monad"
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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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* [[Meet Bob The Monadic Lover]], or the slightly more serious [[The Monadic Way]] |
* [[Meet Bob The Monadic Lover]], or the slightly more serious [[The Monadic Way]] |
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+ | * Computational monads [http://programming.reddit.com/info/ox6s/comments/coxiv part 1] and [http://programming.reddit.com/info/ox6s/comments/coxoh part 2]. |
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+ | * [http://haskell.org/haskellwiki/Books_and_tutorials#Using_monads More tutorials on monads] |
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== Monad Reference Guides == |
== Monad Reference Guides == |
Revision as of 00:53, 13 November 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
See this intuitive explanation of why they should obey the Monad laws.
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.
- Monads as containers
- All About Monads
- Simple monad examples
- Of monads and space suits
- You could have invented monads
- Meet Bob The Monadic Lover, or the slightly more serious The Monadic Way
- Computational monads part 1 and part 2.
- More tutorials on monads
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.
Monad Research
A collection of research papers about monads.
Monads in other languages
Implementations of monads in other languages.
- C++, doc
- CML.event ?
- Clean State monad
- JavaScript
- Java (tar.gz)
- Joy
- LINQ, more, C#, VB
- Lisp
- Miranda
- OCaml, more, also, MetaOcaml
- Perl, Perl6 ?
- Prolog
- Python, and here, and Twisted's Deferred
- Ruby
- Scala, also continuation monad
- Scheme, also
- Tcl
- The Unix Shell
Unfinished:
- Slate
- Parsing, Maybe and Error in Tcl
And possibly there exist:
- Standard ML (via modules?)
Please add them if you know of other implementations.
Collection of links to monad implementations in various languages. on Lambda The Ultimate.
Interesting monads
A list of monads for various evaluation strategies and games:
- Identity monad
- Optional results
- Random values
- Read only state
- Writable state
- Unique supply
- ST
- State
- Undoable state
- Function application
- Error
- Atomic memory transactions
- Continuations
- IO
- Non-deterministic evaluation
- List monad
- Concurrent threads
- Backtracking
- Region allocation
There are many more interesting instance of the monad abstraction out there. Please add them as you come across each species.