このプログラムをjhcにかけると無限ループする気がする

Main_infloop.hs

import Data.Word
import Data.Bits
import Control.Monad
import Foreign.Ptr
import Foreign.Storable

foreign import ccall "c_extern.h Delay" c_delay :: Word32 -> IO ()

gpioPtr :: Ptr Word32
gpioPtr = odr
  where periphBase     = nullPtr        `plusPtr` 0x40000000
        arb2periphBase = periphBase     `plusPtr` 0x10000
        gpioaBase      = arb2periphBase `plusPtr` 0x0800
        odr            = gpioaBase      `plusPtr` 12

gpioOut :: Word32 -> IO ()
gpioOut v = do
  poke gpioPtr v
  c_delay 500000

main :: IO ()
main = mapM_ gpioOut $ cycle pat
  where
    o13 = (1 `shiftL` 13)
    o15 = (1 `shiftL` 15)
    pat = [o13, o13 .|. o15, o15, 0]