[Haskell-cafe] Instance classes and error (also, related to Data.Binary.GET)

Daniel Fischer daniel.is.fischer at web.de
Thu Jan 3 18:48:07 EST 2008


I've no experience with Data.Binary, but I noticed you declared

instance Binary YourType where...

and the compiler says

instance Binary (Get YourType)

is missing. That might be worth looking into.
Cheers,
Daniel

Am Freitag, 4. Januar 2008 00:13 schrieb bbrown:
> I am using the Data.Binary module and having some issues reading big endian
> files (actually, just reading the file).  I can read the header but not the
> rest of the data which contains a set of row information.  Also, go ahead
> and make fun my style of coding.
>
> Anyway, This is the my code and the error at the bottom.
>
>
> The issue stems from here, it says I didn't define an instance, but I did:
>
> instance Binary URLSet where
>     put _ = do BinaryPut.putWord8 0
>     get = do
>       remainingByteData <- BinaryGet.getRemainingLazyByteString
>       i :: URLInfo <- decode remainingByteData
>       j :: TitleInfo <- decode remainingByteData
>       k :: DescrInfo <- decode remainingByteData
>       x :: KeywordsInfo <- decode remainingByteData
>       return (URLSet {urlinfo=i, titleinfo=j,
>                       descrinfo=k, keywordsinfo=x})
>
> -----
>
> module Main where
>
> import Data.Word
> import Data.Binary
> import qualified Data.ByteString.Lazy.Char8 as BSLC8
> import Data.ByteString.Lazy (ByteString)
> import Data.Binary.Get as BinaryGet
> import Data.Binary.Put as BinaryPut
> import IO
> import Text.Printf
> import System.Environment
> import Control.Monad (replicateM, liftM)
>
> {- *********************************************************
>      Define the Database Data Types
>      SpiderDatabase represents a singleton wrapper for an
>      entire database.
>    ********************************************************* -}
> data SpiderDatabase =  SpiderDatabase {
>       magicNumberA :: Word16,
>       magicNumberB :: Word16,
>       majorVers :: Word16,
>       minorVers :: Word16,
>       headerTag :: Word16,
>       poolLen :: Word16,
>       spiderpool :: [URLSet]
>     }
> data URLSet = URLSet {
>       urlinfo :: URLInfo,
>       titleinfo :: TitleInfo,
>       descrinfo :: DescrInfo,
>       keywordsinfo :: KeywordsInfo
> }
> data URLInfo = URLInfo {
>       tag :: Word8,
>       urlid :: Word16,
>       urllen :: Word16,
>       url :: ByteString
> }
> data TitleInfo = TitleInfo {
>       titletag :: Word8,
>       titlelen :: Word16,
>       title :: ByteString
> }
> data DescrInfo = DescrInfo {
>       descrtag :: Word8,
>       descrlen :: Word16,
>       descr :: ByteString
> }
> data KeywordsInfo = KeywordsInfo {
>       keywordstag :: Word8,
>       keywordslen :: Word16,
>       keywords :: ByteString
> }
> {- *********************************************************
>      Class instances
>    ********************************************************* -}
> instance Show SpiderDatabase where
>     show db = let magicb = (magicNumberB db)
>                   header = (headerTag db)
>                   poolct = (poolLen db)
>               in "<<<Database Content>>>\n" ++
>                  (((printf "Magic: %X %X\n") (magicNumberA db))
> (magicNumberB db)) ++
>                  printf "URL Pool Count: %d\n" poolct ++
>                  "<<<End>>>"
>
> instance Binary URLInfo where
>     put _ = do BinaryPut.putWord8 0
>     get = do
>       urltag <- getWord8
>       idx <- getWord16be
>       len <- getWord16be
>       strdata <- BinaryGet.getLazyByteString (fromIntegral len)
>       return (URLInfo {tag=urltag, urlid=idx,
>                        urllen=len, url=strdata})
> instance Binary DescrInfo where
>     put _ = do BinaryPut.putWord8 0
>     get = do
>       tag <- getWord8
>       len <- getWord16be
>       strdata <- BinaryGet.getLazyByteString (fromIntegral len)
>       return (DescrInfo {descrtag=tag,
>                          descrlen=len,
>                          descr=strdata})
> instance Binary TitleInfo where
>     put _ = do BinaryPut.putWord8 0
>     get = do
>       tag <- getWord8
>       len <- getWord16be
>       strdata <- BinaryGet.getLazyByteString (fromIntegral len)
>       return (TitleInfo {titletag=tag,
>                          titlelen=len,
>                          title=strdata})
> instance Binary KeywordsInfo where
>     put _ = do BinaryPut.putWord8 0
>     get = do
>       tag <- getWord8
>       len <- getWord16be
>       strdata <- BinaryGet.getLazyByteString (fromIntegral len)
>       return (KeywordsInfo {keywordstag=tag,
>                             keywordslen=len,
>                             keywords=strdata})
> instance Binary URLSet where
>     put _ = do BinaryPut.putWord8 0
>     get = do
>       remainingByteData <- BinaryGet.getRemainingLazyByteString
>       i :: URLInfo <- decode remainingByteData
>       j :: TitleInfo <- decode remainingByteData
>       k :: DescrInfo <- decode remainingByteData
>       x :: KeywordsInfo <- decode remainingByteData
>       return (URLSet {urlinfo=i, titleinfo=j,
>                       descrinfo=k, keywordsinfo=x})
>
> instance Binary SpiderDatabase where
>     put _ = do BinaryPut.putWord8 0
>     get = do
>       magicnumbera <- BinaryGet.getWord16be
>       magicnumberb <- BinaryGet.getWord16be
>       major <- BinaryGet.getWord16be
>       minor <- BinaryGet.getWord16be
>       header <- BinaryGet.getWord16be
>       poolct <- BinaryGet.getWord16be
>       -- *******************************
>       -- Get the remaining byte string data,
>       -- So that we can use lazy bytestring to load to load the
>       -- the data types.
>       -- *******************************
>       remainingByteData <- BinaryGet.getRemainingLazyByteString
>       -- pool <- (replicate (fromIntegral poolct) (decode
> remainingByteData)) z :: URLSet <- decode remainingByteData
>       return (SpiderDatabase {magicNumberA=magicnumbera,
>                               magicNumberB=magicnumberb,
>                               majorVers=major,
>                               minorVers=minor,
>                               headerTag=header,
>                               poolLen=poolct
>                              })
> main = do
>   putStrLn "Running Spider Database Reader"
>   args <- getArgs
>   db :: SpiderDatabase <- decodeFile (args !! 0)
>   putStrLn $ show db
>   putStrLn "Done"
>
>
> ***
> *** Error:
>
>
> DbReader.hs:119:22:
>     No instance for (Binary (Get URLInfo))
>       arising from a use of `decode' at DbReader.hs:119:22-45
>     Possible fix:
>       add an instance declaration for (Binary (Get URLInfo))
>     In a 'do' expression: i :: URLInfo <- decode remainingByteData
>     In the expression:
>         do remainingByteData <- getRemainingLazyByteString
>            i :: URLInfo <- decode remainingByteData
>            j :: TitleInfo <- decode remainingByteData
>            k :: DescrInfo <- decode remainingByteData
>            ....
>     In the definition of `get':
>         get = do remainingByteData <- getRemainingLazyByteString
>                  i :: URLInfo <- decode remainingByteData
>                  j :: TitleInfo <- decode remainingByteData
>                  ....
>
> DbReader.hs:120:24:
>     No instance for (Binary (Get TitleInfo))
>       arising from a use of `decode' at DbReader.hs:120:24-47
>     Possible fix:
>       add an instance declaration for (Binary (Get TitleInfo))
>     In a 'do' expression: j :: TitleInfo <- decode remainingByteData
>     In the expression:
>         do remainingByteData <- getRemainingLazyByteString
>            i :: URLInfo <- decode remainingByteData
>            j :: TitleInfo <- decode remainingByteData
>            k :: DescrInfo <- decode remainingByteData
>            ....
>     In the definition of `get':
>         get = do remainingByteData <- getRemainingLazyByteString
>                  i :: URLInfo <- decode remainingByteData
>                  j :: TitleInfo <- decode remainingByteData
>                  ....
>
> DbReader.hs:121:24:
>     No instance for (Binary (Get DescrInfo))
>       arising from a use of `decode' at DbReader.hs:121:24-47
>     Possible fix:
>       add an instance declaration for (Binary (Get DescrInfo))
>     In a 'do' expression: k :: DescrInfo <- decode remainingByteData
>     In the expression:
>         do remainingByteData <- getRemainingLazyByteString
>            i :: URLInfo <- decode remainingByteData
>            j :: TitleInfo <- decode remainingByteData
>            k :: DescrInfo <- decode remainingByteData
>            ....
>     In the definition of `get':
>         get = do remainingByteData <- getRemainingLazyByteString
>                  i :: URLInfo <- decode remainingByteData
>                  j :: TitleInfo <- decode remainingByteData
>                  ....
>
> DbReader.hs:122:27:
>     No instance for (Binary (Get KeywordsInfo))
>       arising from a use of `decode' at DbReader.hs:122:27-50
>     Possible fix:
>       add an instance declaration for (Binary (Get KeywordsInfo))
>     In a 'do' expression: x :: KeywordsInfo <- decode remainingByteData
>     In the expression:
>         do remainingByteData <- getRemainingLazyByteString
>            i :: URLInfo <- decode remainingByteData
>            j :: TitleInfo <- decode remainingByteData
>            k :: DescrInfo <- decode remainingByteData
>            ....
>     In the definition of `get':
>         get = do remainingByteData <- getRemainingLazyByteString
>                  i :: URLInfo <- decode remainingByteData
>                  j :: TitleInfo <- decode remainingByteData
>                  ....
>
> DbReader.hs:142:21:
>     No instance for (Binary (Get URLSet))
>       arising from a use of `decode' at DbReader.hs:142:21-44
>     Possible fix: add an instance declaration for (Binary (Get URLSet))
>     In a 'do' expression: z :: URLSet <- decode remainingByteData
>     In the expression:
>         do magicnumbera <- getWord16be
>            magicnumberb <- getWord16be
>            major <- getWord16be
>            minor <- getWord16be
>            ....
>     In the definition of `get':
>         get = do magicnumbera <- getWord16be
>                  magicnumberb <- getWord16be
>                  major <- getWord16be
>                  ....
> make: *** [dbreader] Error 1
>
> --
> Berlin Brown
> [berlin dot brown at gmail dot com]
> http://botspiritcompany.com/botlist/?
>
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