hash-based data structures?

[hrhino]

We've got ISet and ==>>, which are pretty cool, but require an Ord constraint on the key type. Theoretically you can define an ordering for any ADT by considering it a glorified pair of (branch index, values), and use the product ordering. However, given an A => Long hash function, we could implement a hash-trie-based persistent map, such as unordered-containers's.

This could be as simple as closing over an A => Long function, or creating a Hashable typeclass. If we want to go further, having a hash function that accepts a hashing algorithm would allow for potentially more applications of varying strength, although at that point it may be large enough to be considered its own project.

cc @Milyardo @JasnaMRB with whom I chatted last week