project euler 14

euler14.hs

import Criterion.Main

next :: Int -> Int
next n | even n = n `div` 2
       | otherwise = 3*n+1

len :: Int -> Int
len = length . takeWhile (/=1) . iterate next

len' :: Int -> Int -> Int
len' k 1 = k
len' k n = len' (k+1) (next n)

main =
    defaultMain
      [ bgroup "default"
          [ bench "iterate" $ whnf len 350
          , bench "tail recur" $ whnf (len' 1) 350
          ]
      ]

{--
 - warming up
 - estimating clock resolution...
 - mean is 4.375940 us (160001 iterations)
 - found 1174 outliers among 159999 samples (0.7%)
 -   1094 (0.7%) high severe
 -   estimating cost of a clock call...
 -   mean is 1.440690 us (31 iterations)
 -   found 3 outliers among 31 samples (9.7%)
 -     3 (9.7%) high mild
 -
 -     benchmarking default/iterate
 -     mean: 4.302455 us, lb 4.291602 us, ub 4.313241 us, ci 0.950
 -     std dev: 55.30098 ns, lb 47.49248 ns, ub 72.13509 ns, ci 0.950
 -     found 1 outliers among 100 samples (1.0%)
 -     variance introduced by outliers: 5.660%
 -     variance is slightly inflated by outliers
 -
 -     benchmarking default/tail recur
 -     mean: 1.470772 us, lb 1.467614 us, ub 1.474461 us, ci 0.950
 -     std dev: 17.48218 ns, lb 15.19143 ns, ub 20.64320 ns, ci 0.950
 --}