module Main where

import Data.Array
import Data.Array.IO
import Control.Monad
import Control.Monad.Fix
import System


ioaA a s = ioaA' 1 s 0
    where ioaA' i s acc
              | i > sz = return acc
              | True   = do v <- readArray a i
                            writeArray a i (v / s)
                            ioaA' (i+1) s $! (v + acc)
          (_, sz) = Data.Array.IO.bounds a

ioaACPS a s = ioaACPS' 1 s id
    where (_, sz) = Data.Array.IO.bounds a
          ioaACPS' i s acc
           | i > sz = return (acc 0)
           | True   =
               do v <- readArray a i
                  writeArray a i (v/s)
                  ioaACPS' (i+1) s (\x -> v + acc x)


main = do
  [method,n] <- getArgs
  (a::IOArray Int Double) <- newListArray (1::Int,read n) [(1::Double)..read n]
  if method == "fix"
    then mfix (\ ~s -> ioaA a s) >> return ()
    else if method == "cps"
           then mfix (\ ~s -> ioaACPS a s) >> return ()
           else if method == "loop"
                  then normLoop a
                  else norm a
  return ()

norm a = do
  t <- foldM (\t i -> (t+) `liftM` readArray a i) 0 [1..sz]
  mapM_ (\i -> readArray a i >>= writeArray a i . (/t)) [1..sz]
  where (_,sz) = Data.Array.IO.bounds a

normLoop a = do t <- normLoop' 1 0
                normLoop'' 1 t
    where normLoop' i acc
              | i > sz = return acc
              | True   = do v <- readArray a i
                            normLoop' (i+1) $! (v + acc)
          normLoop'' i t
              | i > sz = return ()
              | True   = do v <- readArray a i
                            writeArray a i (v/t)
                            normLoop'' (i+1) t
          (_, sz) = Data.Array.IO.bounds a

{-
        |       FIXIO        |                  TWO LOOPS
        |  fix       cpsfix  |   map/fold    loop    unboxed-m/f  unboxed-loop
--------+--------------------+--------------------------------------------------
 100000 |  0.71       1.37   |     1.60      1.61       0.90          0.42      
 250000 |  6.51       5.74   |     7.48      7.24       2.90          1.22      
 500000 | 23.88      21.32   |    25.35     26.38       7.51          2.27      
1000000 | 92.72      79.16   |    97.83    105.73      21.78          4.54      
-}