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{-# LANGUAGE ExistentialQuantification #-}
-- The second version (count2) took ages with GHC 6.12
-- because the typeOf function was not properly memoised
import Data.Typeable
import System.CPUTime
size :: Int
size = 40000 -- This was big enough to take 5 seconds in
-- the bad case on my machine.
data Any = forall a. (Typeable a) => Any a
int_type, int_list_type :: TypeRep
int_type = typeOf (undefined :: Int)
int_list_type = typeOf (undefined :: [Int])
count1 :: [Any] -> Int
count1 [] = 0
count1 (Any x:xs) = count1 xs + (if typeOf x == int_type then 1 else 0)
doTime x = do
start <- getCPUTime
putStr "Result: "
print x
stop <- getCPUTime
putStr "Time(sec): "
print (round $ fromIntegral (stop - start) / 1e12)
-- The 'round' rounds to an integral number of seconds
-- Should be zero if things are working right!
main = do
let list = [MkT | i <- [1..size :: Int]]
putStrLn "count1"
let x = map Any list
doTime $ count1 x
doTime $ count1 x
doTime $ count1 x
putStrLn ""
putStrLn "count2"
let x = map (Any . (:[])) list
doTime $ count1 x
doTime $ count1 x
doTime $ count1 x
data T = MkT
tcname :: TyCon
tcname = mkTyCon "T"
instance Typeable T where { typeOf _ = mkTyConApp tcname [] }
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