[Haskell-cafe] Num instance for Lazy ByteStrings (was: NumLazyByteString Package License)

Henning Thielemann schlepptop at henning-thielemann.de
Wed Mar 10 06:16:12 EST 2010

Yitzchak Gale schrieb:
> Henning Thielemann wrote:
>>> Is NumLazyByteString a newtype around Bytestring.Lazy
>>> that interprets the bit stream represented by the ByteString
>>> as integer?
> Thomas DuBuisson wrote:
>> Not exactly.  There is not newtype wrapper.  NumLazyByteString is:
>> instance Num L.ByteString where
>>  ...
> Are you absolutely certain that this is the one and only
> canonical instance that can ever exist that makes sense?
> Otherwise, please use a newtype wrapper.
I think there are at least two reasonable instance: One that treats all 
bytes individually and one that treats the whole bytestring as one 
binary number.

Btw. I assume that in order to be lazy when computing exactly with 
integers you must start with the least significant bits, right? In my 
implementation of Positional numbers I start with the most significant 
digits since I implemented fractional numbers and I must use a redundant 
set of digits in order to stay lazy in case of carries.
> The reason for this is one of the few remaining major warts
> in Haskell - that there is absolutely *no way* to
> prevent the export of instances from a module that you import.
Since this is a common issue a wrote a Wiki article on it:

More information about the Haskell-Cafe mailing list