Data Structures in Clojure: Hash Tables

I love these posts. Even though I'd never use this in production, it's an excellent intro to the same basic data structure taught everywhere. But instead of mucking with a templated C++ implementation (or getting lost in the "plain cons cells for everything!" weeds)... Clojure! It also shows that as much as idiomatic Clojure frowns on OOP and mutability... it's not really that unpleasant to read. I almost want to go through all my old C++ assignments and redo them in Clojure like this.

> On the machine this was implemented, insertion speed increased ~110x, compared with the non-hinted implementation.

That makes it sound like type hints are essentially mandatory for anything where performance matters.

Nice article! It would have been interesting to see how it fares against something like java.util.HashMap.

Where is the definition of the actual hash function? That is the interesting and tricky part of a hash table. Is "hash" a Clojure built-in?

Very nitpicky but I find the ligatures on all the "t" characters very distracting.

Additionally, I don't know Closure, but are there any default hash-table implementations? If so, how does this implementation compare against the base one?