[Haskell-cafe] ByteString.pack behavior
dons at galois.com
Mon May 19 14:22:06 EDT 2008
Safe Num wrappers for primitive types that throw exceptions on overflow
would make a useful library.
> 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
> Czech Republic
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