Benchmarking of build-in length and custom length function using criterion

lengthbench.hs

{-
Benchmarking of build-in length and custom length function using criterion.

Compile with the command: ghc -O3 -W --make lengthbench.hs -o lengthbench

Results (timings in seconds, std. dev. negligible):
build-in length:
      1000000	0.004
      2000000	0.009
      4000000	0.016
      8000000	0.035
     16000000	0.082
     32000000	0.162
     64000000	0.322

custom length (klength):
      1000000   0.014
      2000000   0.026
      4000000   0.046
      8000000   0.078
     16000000   0.128
     32000000   0.198
     64000000	0.316
-}
import qualified Criterion.Main as C
import Data.List (foldl')

makeList :: Int -> [Int]
makeList n = take n ones
  where ones = 1 : ones

klength :: [a] -> Int
klength ls = foldl' (\n _ -> n+1) 0 ls

main :: IO()
main = do
  C.defaultMain
    [ C.bench "length 1000000"  $ C.whnf length (makeList 1000000)
    , C.bench "length 2000000"  $ C.whnf length (makeList 2000000)
    , C.bench "length 4000000"  $ C.whnf length (makeList 4000000)
    , C.bench "length 8000000"  $ C.whnf length (makeList 8000000)
    , C.bench "length 16000000" $ C.whnf length (makeList 16000000)
    , C.bench "length 32000000" $ C.whnf length (makeList 32000000)
    , C.bench "length 64000000" $ C.whnf length (makeList 64000000)

    , C.bench "klength 1000000"  $ C.whnf klength (makeList 1000000)
    , C.bench "klength 2000000"  $ C.whnf klength (makeList 2000000)
    , C.bench "klength 4000000"  $ C.whnf klength (makeList 4000000)
    , C.bench "klength 8000000"  $ C.whnf klength (makeList 8000000)
    , C.bench "klength 16000000" $ C.whnf klength (makeList 16000000)
    , C.bench "klength 32000000" $ C.whnf klength (makeList 32000000)
    , C.bench "klength 64000000" $ C.whnf klength (makeList 64000000)
    ]