Yes, this is obvious B.pack :: [GHC.Word.Word8] -> B.ByteString So, in B.pack $ encode' [1..100] GHCi expects "encode' [1..100]" to be of type [GHC.Word.Word8] Now, your encode' has type encode' :: Integral a => [a] -> [a] So, in encode' definition, all calculations are in Word8. Now, (256 :: Word8) is zero. No wonder you get a "divide by zero" error when trying to calculate "something `mod` 256" On 19 May 2008, at 00:14, Dušan Kolář wrote:
Hello all,
Maybe there is something obvious I can't see, but I have this behavior for 6.8.2 ghci:
$ghci ttest1p.hs GHCi, version 6.8.2: http://www.haskell.org/ghc/ :? for help Loading package base ... linking ... done. [1 of 1] Compiling Main ( ttest1p.hs, interpreted ) Ok, modules loaded: Main. *Main> encode' [1..100] Loading package array-0.1.0.0 ... linking ... done. Loading package bytestring-0.9.0.1 ... linking ... done. [1,0,2,0,3,0,4,0,5,0,6,0,7,0,8,0,9,0,10,0,11,0,12,0,13,0,... // deleted *Main> B.pack [0..100] "\NUL\SOH\STX\ETX\EOT\ENQ\ACK\a\b\t\n\v\f\r\SO\SI\DLE \DC1\DC2\DC3\DC4\NAK\SYN\ETB\CAN\EM\SUB\ESC\FS\GS\RS\US !\"#$%&'()* +,-./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?
Thanks for any hint,
Dusan
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