Basic I/O performance in Haskell

Question

Another microbenchmark: Why is this \"loop\" (compiled with ghc -O2 -fllvm, 7.4.1, Linux 64bit 3.2 kernel, redirected to /dev/null)

Answer 1

The standard Haskell way to hand giant bytestrings over to the operating system is to use a builder monoid.

import Data.ByteString.Lazy.Builder  -- requires bytestring-0.10.x
import Data.ByteString.Lazy.Builder.ASCII -- omit for bytestring-0.10.2.x
import Data.Monoid
import System.IO

main = hPutBuilder stdout $ build  [0..100000000::Int]

build = foldr add_line mempty
   where add_line n b = intDec n <> charUtf8 '\n' <> b

which gives me:

 $ time ./printbuilder >> /dev/null
 real   0m7.032s
 user   0m6.603s
 sys    0m0.398s

in contrast to Haskell approach you used

$ time ./print >> /dev/null
real    1m0.143s
user    0m58.349s
sys 0m1.032s

That is, it's child's play to do nine times better than mapM_ print, contra Daniel Fischer's suprising defeatism. Everything you need to know is here: http://hackage.haskell.org/packages/archive/bytestring/0.10.2.0/doc/html/Data-ByteString-Builder.html I won't compare it with your C since my results were much slower than Daniel's and n.m. so I figure something was going wrong.

Edit: Made the imports consistent with all versions of bytestring-0.10.x It occurred to me the following might be clearer -- the Builder equivalent of unlines . map show:

main = hPutBuilder stdout $ unlines_ $ map intDec [0..100000000::Int]
 where unlines_ = mconcat . map (<> charUtf8 '\n')