[Haskell-cafe] ByteString.pack behavior

[Don Stewart]

Safe Num wrappers for primitive types that throw exceptions on overflow
would make a useful library.

Any takers?

-- Don

kolar:
> 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
> 
> Dusan
> 
> Don Stewart wrote:
> >kolar:
> >  
> >>Hello all,
> >>
> >> Maybe there is something obvious I can't see, but I have this behavior 
> >>for 6.8.2 ghci:
> >>
> >>$ghci ttest1p.hs
> >>GHCi, version 6.8.2: http://www.haskell.org/ghc/  :? for help
> >>Loading package base ... linking ... done.
> >>[1 of 1] Compiling Main             ( ttest1p.hs, interpreted )
> >>Ok, modules loaded: Main.
> >>*Main> encode' [1..100]
> >>Loading package array-0.1.0.0 ... linking ... done.
> >>Loading package bytestring-0.9.0.1 ... linking ... done.
> >>[1,0,2,0,3,0,4,0,5,0,6,0,7,0,8,0,9,0,10,0,11,0,12,0,13,0,... // deleted
> >>*Main> B.pack [0..100]
> >>"\NUL\SOH\STX\ETX\EOT\ENQ\ACK\a\b\t\n\v\f\r\SO\SI\DLE\DC1\DC2\DC3\DC4\NAK\SYN\ETB\CAN\EM\SUB\ESC\FS\GS\RS\US 
> >>!\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcd"
> >>*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
> 
> --
>