"Duplicate instance declarations"

[Bulat Ziganshin]

Hello Ashley,

Wednesday, December 28, 2005, 1:56:51 AM, you wrote:

i tried to implement your solution and failed. i will extend my
original example to show you my problem:

>> class BufStream h where
    vPutBuf :: h -> Ptr a -> Int -> IO ()

>> class CharStream h where
    vPutStr :: h -> String -> IO ()

>> instance (CharStream h) => BufStream h where
    vPutBuf h buf len =
        do str <- peekCStringLen (castPtr buf, len)
           vPutStr h str

>> class MemoryStream h where
>> instance (MemoryStream h) => BufStream h where

AY> Try this:

class BufStream h where
    vPutBuf :: h -> Ptr a -> Int -> IO ()

class (BufStream h) => CharStream h where
    vPutStr :: h -> String -> IO ()

now i can give default implemetation of `vPutStr` via `vPutBuf`. but i
need to implement `vPutBuf` via `vPutStr`!

AY> class (BufStream h) => MemoryStream h where

the same problem here - i need to implement `vPutBuf` via functions of
MemoryStream, but it's impossible




-- 
Best regards,
 Bulat                            mailto:bulatz at HotPOP.com