WeakSets

Simple set types. Useful to create sets of arbitrary types and nested sets.

This package answers two problems : how to make sets and maps of types which do not implement the Ord typeclass and how to make arbitrarily nested sets as set theory allows. The problems are resolved thanks to WeakSets and WeakMaps. A WeakSet is like a list where duplicates are considered the same when testing for equality. A WeakMap is a set of couples (key,value).