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:;<=>[EMAIL PROTECTED]"
*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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