I always liked Common Lisp for this, since you could so easily inspect data structures like hashes at run time. I think CMUCL had a really interesting and uniq

I always liked Common Lisp for this, since you could so easily inspect data structures like hashes at run time. I think CMUCL had a really interesting and unique hash implementation that relied on two identically sized arrays, one for the keys and data, and another for a "next" index that showed you where to go for a key collision.