# New monads

### From HaskellWiki

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View [[New monads/MonadAdvSTM]]. |
View [[New monads/MonadAdvSTM]]. |
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+ | == TimedStateT == |
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+ | Like StateT, but will force an early return once a certain time duration is exceeded. |
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+ | http://www.mapcar.org/haskell/TimedStateT/ |
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[[Category:Idioms]] |
[[Category:Idioms]] |

## Revision as of 04:35, 12 December 2006

## Contents |

Remember to add a [ [ Category:Code ] ] tag to any new sub-pages.

## 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.

### 4.1 MonadRandomSplittable

A refinement of MonadRandom to integrate RandomGen's split function.

View at New monads/MonadRandomSplittable

## 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.

## 9 MonadAdvSTM

Here is an extension of STM to easy interaction with IO after committing or retrying. Inspired by Simon P-J.

View New monads/MonadAdvSTM.

## 10 TimedStateT

Like StateT, but will force an early return once a certain time duration is exceeded.