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