Can I easily fix the modifyIORef statement by swapping "something" ? --Joerg On Jul 18, 2013, at 7:19 PM, "Edward Z. Yang" wrote:

shiftL has the wrong type: Bits a => a -> Int -> a so it is expecting the value in the IORef to be an Int.

Edward

Excerpts from Joerg Fritsch's message of Thu Jul 18 10:08:22 -0700 2013:

...

All, what is wrong w the below code?

I get an type error related to the operation shiftL

import Data.Bits import Data.Word import Data.IORef

data Word32s = Word32s { x :: IORef Word32 }

bitfield :: Word32 bitfield = 0

mkbitfield :: Word32 -> IO Word32s mkbitfield i = do the_bf <- newIORef i return (Word32s the_bf)

sLbitfield :: Integer -> Word32s -> IO () sLbitfield i (Word32s bf) = do modifyIORef bf (shiftL i)

main::IO() main = do oper_bf <- mkbitfield bitfield sLbitfield 2 oper_bf

bf_003.hs:15:48: Couldn't match type `Int' with `Word32' Expected type: Word32 -> Word32 Actual type: Int -> Word32 In the return type of a call of `shiftL' In the second argument of `modifyIORef', namely `(shiftL i)' In a stmt of a 'do' block: modifyIORef bf (shiftL i)

bf_003.hs:15:55: Couldn't match expected type `Word32' with actual type `Integer' In the first argument of `shiftL', namely `i' In the second argument of `modifyIORef', namely `(shiftL i)' In a stmt of a 'do' block: modifyIORef bf (shiftL i)

Thanks, --Joerg