# New monads

### From HaskellWiki

BrettGiles (Talk | contribs) m (NewMonads moved to New monads) |
BrettGiles (Talk | contribs) (Change links, add monad category) |
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It seems that the liftIO function from MonadIO can be generalized to access whatever the base of a transformer stack happens to be. So there is no need for a liftSTM, liftST, etc. |
It seems that the liftIO function from MonadIO can be generalized to access whatever the base of a transformer stack happens to be. So there is no need for a liftSTM, liftST, etc. |
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− | View [[NewMonads/MonadBase]]. |
+ | View [[New monads/MonadBase]]. |

== MonadLib == |
== MonadLib == |
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== LazyWriterT == |
== LazyWriterT == |
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− | This came up on the mailing list: Why is WriterT never lazy? The answer is it does not use lazy patterns with "~". So here is a more useful [[NewMonads/LazyWriterT]] that add two "~" to the definition of (>>=) and renames WriterT to LazyWriterT. |
+ | This came up on the mailing list: Why is WriterT never lazy? The answer is it does not use lazy patterns with "~". So here is a more useful [[New monads/LazyWriterT]] that add two "~" to the definition of (>>=) and renames WriterT to LazyWriterT. |

== MonadRandom == |
== MonadRandom == |
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A simple monad transformer to allow computations in the transformed monad to generate random values. |
A simple monad transformer to allow computations in the transformed monad to generate random values. |
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− | View [[NewMonads/MonadRandom]]. |
+ | View [[New monads/MonadRandom]]. |

== MonadSupply == |
== MonadSupply == |
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Here is a simple monad/monad transformer for computations which consume values from a (finite or infinite) supply. Note that due to pattern matching, running out of supply in a non-MonadZero monad will cause an error. |
Here is a simple monad/monad transformer for computations which consume values from a (finite or infinite) supply. Note that due to pattern matching, running out of supply in a non-MonadZero monad will cause an error. |
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− | View [[NewMonads/MonadSupply]]. |
+ | View [[New monads/MonadSupply]]. |

== MonadUndo == |
== MonadUndo == |
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Here is a modified state monad transformer for keeping track of undo/redo states automatically. |
Here is a modified state monad transformer for keeping track of undo/redo states automatically. |
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− | View [[NewMonads/MonadUndo]]. |
+ | View [[New monads/MonadUndo]]. |

== MonadUnique == |
== MonadUnique == |
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This is a simple (trivial) monad transformer for supplying unique integer values to an algorithm. |
This is a simple (trivial) monad transformer for supplying unique integer values to an algorithm. |
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− | View [[NewMonads/MonadUnique]]. |
+ | View [[New monads/MonadUnique]]. |

== MonadSTO == |
== MonadSTO == |
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Here's an extension of the ST monad in which the references are ordered and showable (they list their creation index). |
Here's an extension of the ST monad in which the references are ordered and showable (they list their creation index). |
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− | View [[NewMonads/MonadSTO]]. |
+ | View [[New monads/MonadSTO]]. |

[[Category:Idioms]] |
[[Category:Idioms]] |
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+ | [[Category:Monad]] |

## Revision as of 16:02, 7 October 2006

## Contents |

## 1 MonadBase

It seems that the liftIO function from MonadIO can be generalized to access whatever the base of a transformer stack happens to be. So there is no need for a liftSTM, liftST, etc.

View New monads/MonadBase.

## 2 MonadLib

This is by Iavor S. Diatchki and can be found at http://www.cse.ogi.edu/~diatchki/monadLib/

It is a new version of the mtl package with transformers: ReaderT WriterT StateT ExceptT SearchT ContT

It also defines BaseM which is like MonadBase above.

## 3 LazyWriterT

This came up on the mailing list: Why is WriterT never lazy? The answer is it does not use lazy patterns with "~". So here is a more useful New monads/LazyWriterT that add two "~" to the definition of (>>=) and renames WriterT to LazyWriterT.

## 4 MonadRandom

A simple monad transformer to allow computations in the transformed monad to generate random values.

View New monads/MonadRandom.

## 5 MonadSupply

Here is a simple monad/monad transformer for computations which consume values from a (finite or infinite) supply. Note that due to pattern matching, running out of supply in a non-MonadZero monad will cause an error.

View New monads/MonadSupply.

## 6 MonadUndo

Here is a modified state monad transformer for keeping track of undo/redo states automatically.

View New monads/MonadUndo.

## 7 MonadUnique

This is a simple (trivial) monad transformer for supplying unique integer values to an algorithm.

View New monads/MonadUnique.

## 8 MonadSTO

Here's an extension of the ST monad in which the references are ordered and showable (they list their creation index).

View New monads/MonadSTO.