ezyang:
Hey guys, an update!
It turns out, Clojure is using mutation under the hood during its initial data structure generation to make populating the hash-map blazingly fast. When I force it to use the purely functional interface, the performance is much closer to Haskell's.
Haskell Clojure 128K 0.56s 0.33s 256K 1.20s 0.84s 512K 2.62s 2.80s
There's a large amount of variance in the Java samples, as HotSpot kicks in; they appear to start off with identical performance and then the Clojure implementation steadily performs better as the JVM optimizes away.
I'd be really curious about techniques that permit mutation during the construction of functional datastructures; this seems like a cool way to get fast performance w/o giving up any of the benefits of immutability. Unfortunately, my (admittedly short) experiments in this domain ran up against the difficulty that vector didn't let me unsafely freeze its mutable version. :-)
Almost all the vector library generators fill a vector destructively, before doing an unsafeFreeze. Here's an example of filling a buffer with randoms, random g n = do v <- GM.new n fill v 0 G.unsafeFreeze v where fill v i | i < n = do x <- R.random g GM.unsafeWrite v i x fill v (i+1) | otherwise = return ()