# New monads

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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. | ||

− | View [[ | + | View [[New monads/MonadBase]]. |

== MonadLib == | == MonadLib == | ||

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== LazyWriterT == | == 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 [[ | + | 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. | ||

− | View [[ | + | 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. | ||

− | View [[ | + | 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. | ||

− | View [[ | + | 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. | ||

− | View [[ | + | 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). | ||

− | View [[ | + | View [[New monads/MonadSTO]]. |

[[Category:Idioms]] | [[Category:Idioms]] | ||

+ | [[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.