Dusan Kolar wrote:

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...

While doing that is easy in this case, it becomes quite delicate in the general case. More precisely, it grows into the halting problem. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited.

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@fit.vutbr.cz Brno 612 66 Czech Republic

--

On Mon, May 19, 2008 at 9:44 PM, Antoine Latter wrote:

Sounds like fun. Neither the error messages nor the code will be pretty.

Are we just interested in the Data.Int types and the Data.Word types?

It's up on hackage here: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/checked I'm not sure how easy it would be to track down the error once you get it, but I suppose knowing is better than not knowing. I haven't made any attempt towards making the bounds-checking cheap, so this isn't a solution for deploying an application which needs fast integer operations with bounds checking. This is more for testing or verification. Let me know if you find this useful, or if you think it needs any work. -Antoine

aslatter:

On Tue, May 20, 2008 at 8:44 AM, Antoine Latter wrote:

...

It's up on hackage here: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/checked

One more thing - there's no "Data" instance for these types. Presumably it wouldn't be hard to add, I just wasn't familiar with the class, and the technique (if any) for lifting an instance of Data through a newtype wasn't immediately obvious form the class interface.

With generalised newtype deriving, it should be fine to derive Data and Typeable: {-# LANGUAGE DeriveDataTypeable #-} {-# LANGUAGE GeneralizedNewtypeDeriving #-} module M where import Data.Generics newtype T = T Int deriving (Eq,Ord,Show,Read,Bounded,Enum,Num,Data,Typeable) x :: T x = 1 + 2 -- Don