# The Cardinality package

This module introduces typeclasses

`HasCard`= "Has cardinality". In other words, "it's possible to measure current count of elements for this container"`HasCardT`= "Has cardinality (for container types of kind`(* -> *)`)". In other words, "it's possible to measure current count of elements for this container (for container types of kind`(* -> *)`)"`HasCardConstr`= "Has cardinality constraint". In other words, "there is a capacity constraint for this container".`HasCardConstrT`= "Has cardinality constraint (for container types of kind`(* -> *)`)". In other words, "there is a capacity constraint for this container type of kind`(* -> *)`".`HasCardUCT`= "Has cardinality-unsafe container transform". Define transform that may thow an error, if contents of`from`don't fit in`to`.`HasCardUCT_T`= "Has cardinality-unsafe container transform (for container types of kind`(* -> *)`)". Same thing as`HasCardUCT`, but for containers of kind`(* -> *)`.

No, it's not about playing cards. It's about cardinalities.
Wikipedia: "/In mathematics, the cardinality of a set is a measure of
the number of elements of the set. For example, the set A =
2, 4, 6
contains 3 elements, and therefore A has a cardinality of 3./"
In this package I dare to extend the definition a bit to
"*C. is a measure of the number of elements in a container*"

Usual containers are (together with their cardinality ranges):

`Identity a`(1 element)`Maybe a`(0..1 element)`[a]`(0..inf elements)`Map k e`(0..inf elements)

I extended this to the folowing list:

`EmptySet a`(0 elements)`Identity a`(1 element)`Maybe a`(0..1 element)`[a]`(0..inf elements)`NeverEmptyList a`(1..inf elements)`Map k e`(0..inf elements)

Typeclass `HasCardUCT` together with function `sContTrans`
(safe container transform) provides a facility to safely change
container from one to another keepeng the content. If content doesn't
fit to target container, `Nothing` is returned. However, when
transforming from list `[a]` to `(Maybe a)` it won't check list length
further first 2 elements. The complexity and power of this package is
that it provides a facility to *lazily* evaluate amount of content in
the container.

To interface package functions

import Data.Cardinality

## Properties

Versions | 0.1, 0.2 |
---|---|

Dependencies | base (==4.*), containers, mtl [details] |

License | LGPL |

Copyright | Copyright (c) 2010 Andrejs Sisojevs |

Author | Andrejs Sisojevs <andrejs.sisojevs@nextmail.ru> |

Maintainer | Andrejs Sisojevs <andrejs.sisojevs@nextmail.ru> |

Stability | experimental |

Category | Data |

Uploaded | Wed Jan 20 13:19:09 UTC 2010 by AndreySisoyev |

Distributions | NixOS:0.2 |

Downloads | 676 total (6 in the last 30 days) |

Votes | |

Status | Docs uploaded by user Build status unknown [no reports yet] |

## Downloads

- Cardinality-0.2.tar.gz [browse] (Cabal source package)
- Package description (included in the package)