[Haskell-cafe] Why is Haskell so slow (comparing to Java/Scala)?

[Станислав Черничкин]

I've wrote simple Haskell benchmark program, which populated primitive
vector from vector package:

import           Data.Vector.Primitive.Mutable as P

vectorBench :: Benchmark
vectorBench = bgroup "vector" [ primitive ]
  where
    primitive = bgroup "primitive" [ write1M ]
      where
        write1M =  bench "write1M" $ nfIO $ do
          v <- P.unsafeNew 1000000
          void $ for [0..1000000 - 1] $ flip (P.unsafeWrite v) (1 :: Int)
          return ()

I use `unsafeNew` to skip memory initialization and `unsafeWrite` to skip
boundary checks, I guess it's fastest possible way to write something to
vector. My result was about 40 ms.

I wrote similar program in Scala:

for (_ <- 1 to 5) {
  val start = System.currentTimeMillis()
  val a = new Array[Long](1000000)
  for (i <- 0 until 1000000) {
    a(i) = 1L
  }
  val end = System.currentTimeMillis()
  println(s"${end - start} ms")
}

I skip neither boundary checks nor memory initialization, I also used
generic array here (suitable for any types of objects, not just for
primitive types), so I expected longer run time. But what I got was
shocking:

7 ms
3 ms
2 ms
1 ms
2 ms

This program runs 20-40 times faster than Haskell after warm-up. 20-40
times, Carl! Why is Haskell soo slooooow? How can it be?


-- 
Sincerely, Stanislav Chernichkin.
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