[Haskell-cafe] ByteString.pack behavior
kolar at fit.vutbr.cz
Mon May 19 00:25:42 EDT 2008
Thanks. I've realized that as soon as I was in my bed. ;-)
Nevertheless, a question comes to me - shouldn't compiler report a
warning? I know it cannot in the current state, but it should. :-) Quite
dummy C compilers tell me I'm "loosing significant digits of number
literals" if I'm doing that. Maybe, already seen in some other thread
some time ago, the compiler should be less general/should know more
about data types...
Thanks and regards
Don Stewart wrote:
>> Hello all,
>> Maybe there is something obvious I can't see, but I have this behavior
>> for 6.8.2 ghci:
>> $ghci ttest1p.hs
>> GHCi, version 6.8.2: http://www.haskell.org/ghc/ :? for help
>> Loading package base ... linking ... done.
>> [1 of 1] Compiling Main ( ttest1p.hs, interpreted )
>> Ok, modules loaded: Main.
>> *Main> encode' [1..100]
>> Loading package array-0.1.0.0 ... linking ... done.
>> Loading package bytestring-0.9.0.1 ... linking ... done.
>> [1,0,2,0,3,0,4,0,5,0,6,0,7,0,8,0,9,0,10,0,11,0,12,0,13,0,... // deleted
>> *Main> B.pack [0..100]
>> *Main> B.pack $ encode' [1..100]
>> "*** Exception: divide by zero
>> where ttest1p.hs:
>> import qualified Data.ByteString as B
>> encode'  = 
>> encode' (x:xs) =
>> if x==0 then 0:0:encode' xs
>> else (x `mod` 256) : (x `div` 256) : encode' xs
>> What is the difference, except list length and value structure? Where is
>> my error?
> ByteStrings take Word8 values as input, so x `div` 256 , where 256 ::
> Word8, overflows to 0.
> -- Don
Dusan Kolar tel: +420 54 114 1238
UIFS FIT VUT Brno fax: +420 54 114 1270
Bozetechova 2 e-mail: kolar at fit.vutbr.cz
Brno 612 66
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