[Haskell-beginners] Compile type Error

[Rafael Gustavo da Cunha Pereira Pinto]

I didn't compile, but, by the looks of it, I would change

import qualified Data.ByteString as BS (readFile)

for

import qualified Data.ByteString.Lazy as BS (readFile)


as it seems sha1 needs a lazy bytestring

On Thu, Jan 29, 2009 at 13:25, emmanuel.delaborde <
emmanuel.delaborde at cimex.com> wrote:

> Hello
>
> I have the following snippet :
>
> ----------------------------------------------------------
>
> module Main where
>
> import System.Environment (getArgs)
> import Data.Digest.OpenSSL.MD5 (md5sum)
> import Data.Digest.Pure.SHA (sha1, showDigest)
> import qualified Data.ByteString as BS (readFile)
>
> -- sha1 :: ByteString -> Digest
> -- readFile :: FilePath -> IO ByteString
> -- md5sum :: ByteString -> String
> -- showDigest :: Digest -> String
>
> checkHash :: String -> String -> String -> IO ()
> checkHash codec hash file =
>  let f = case codec of
>            --"md5"  -> md5sum
>            "sha1" -> showDigest . sha1
>            _      -> error "Codec must be md5 or sha1 !" in
>  BS.readFile file >>= \fileBS ->
>  let fileHash = f fileBS in
>  print (hash == fileHash)
>
> main =
>  getArgs >>= \as ->
>  case as of
>    (codec:hash:file:_) -> checkHash codec hash file
>    _                    -> usage
>
> usage = print "checksum codec hash file"
>
> ----------------------------------------------------------
>
> which fails to compile, this is the error I get :
>
>
> checksum.hs:20:19:
>    Couldn't match expected type `Data.ByteString.Lazy.Internal.ByteString'
>           against inferred type `Data.ByteString.Internal.ByteString'
>    In the first argument of `f', namely `fileBS'
>    In the expression: f fileBS
>    In the definition of `fileHash': fileHash = f fileBS
>
>
>
>
> it looks like  (showDigest . sha1) expects
> Data.ByteString.Lazy.Internal.ByteString but gets
> Data.ByteString.Internal.ByteString
>
> What can I do ?
>
> Thanks
>
> E.
>
>
>
>
>
>
>
>
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-- 
Rafael Gustavo da Cunha Pereira Pinto
Electronic Engineer, MSc.
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