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{-# LANGUAGE BangPatterns #-}
{-# OPTIONS -fvia-C -optc-O3 -fexcess-precision -optc-msse3 #-}
import Control.Monad.ST
import Data.Array.ST
import Data.Array.Base
main = print $ runST
(do arr <- newArray (1,2000000) 137.0 :: ST s (STUArray s Int Double)
go arr 2000000 0.0 )
go :: STUArray s Int Double -> Int -> Double -> ST s Double
go !a i !acc
| i < 1 = return acc
| otherwise = do
b <- unsafeRead a i
unsafeWrite a i (b+3.0)
c <- unsafeRead a i
go a (i-1) (c+acc)
|
