In fact, a good friend of mine is working to put scala bindings over all the clojure data structures so they can be used transparently in scala. They're that good.
Wrapping the PersistentMaps took like less than 200 lines of code: http://github.com/codahale/yoink
From my point of view 200 LoC giving me something I already have is a lot. From the point of view of your friend 200 LoC might be a very small price to pay for a good learning experience.
I'm also slightly confused as to why you think reusing stable, proven, and reviewed data structure implementations is a "good learning experience" as opposed to being SOP.
In contrast, Clojure's PersistentHashMap dates back to 2007 and was in both the 1.0 and 1.1.0 releases.
In the meantime, I benchmarked Yoink's PeristentHashMap against 2.8.0.RC2's immutable.HashMap by a) creating a map of 100,000 sequential keys and then removing them all, and b) creating a map of 100,000 random keys and then removing 100,000 random keys. In the first case, Yoink was 20.7041% (±1.83693%) faster. In the second case, Yoink was 24.7834% (±4.17055%) faster. (Student's t distribution, 95% confidence interval, source is in src/test on the GitHub project and I used ministat for the statistical analysis [a cross-platform port of which is also available on my GitHub page].)
So to summarize, I have a provably faster hash array mapped trie at almost zero cost right now because I spent a few hours with a "good learning experience."
What I wanted to confer was that, you _might_ have been wasting a lot of effort because I assumed that you might not have been informed about work of the Scala team that has a high likelihood of obsoleting your project in the near future. Obviously you were informed and my notice was inappropriate. Be assured it won't happen again.
If increasing the performance by about 1/4 for your use cases - compared to the current beta - is valuable for you, great! For me it wouldn't have been worth a few hours. 'A good learning experience' would have. But obviously your values are different.
I just wanted to point out the (for me at least) non obvious fact that the mind behind the theory of Clojure's persistent datastructures is working on Scala's collection library and that Scala's hash maps are already backed by hash tries - http://www.scala-lang.org/archives/downloads/distrib/files/n...
And it's pretty neat to see a scala proponent call a scala project a "waste of time." Way to represent for your community, bro.