Map package:stm-containers

Hash-table, based on STM-specialized Hash Array Mapped Trie.
Bidirectional map. Essentially, a bijection between subsets of its two argument types. For one value of the left-hand type this map contains one value of the right-hand type and vice versa.
A multimap, based on an STM-specialized hash array mapped trie. Basically it's just a wrapper API around Map key (Set value).