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{-# LANGUAGE ForeignFunctionInterface #-}
{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE TypeOperators #-}
-- The idea:
--
-- 1. Register a CAFfy foreign export
-- 2. Force a CAF reachable from the export
-- 3. Do a GC
-- 4. Then call the foreign export.
import System.Mem
import Foreign.C.Types
x :: Integer
x = fib 80
{-# NOINLINE x #-}
test_export :: IO CInt
test_export = return $ fromIntegral x
fib :: Int -> Integer
fib 0 = 1
fib 1 = 1
fib n = go 1 1 n
where
go :: Integer -> Integer -> Int -> Integer
go !n0 !n1 0 = n1
go n0 n1 i = let n0' = n1
n1' = n0 + n1
in go n0' n1' (i-1)
{-# NOINLINE fib #-}
foreign export ccall test_export :: IO CInt
foreign import ccall test :: IO CInt
main :: IO ()
main = do
print (fromIntegral x :: CInt)
_ <- return $! fib 100000
performMajorGC
test >>= print
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