[Haskell-cafe] curious about sum

Keith Sheppard keithshep at gmail.com
Sat Jun 13 10:47:46 EDT 2009


That's an interesting example. I guess a lazy number system like that
would work nicely for Deniz's use case.

On Sat, Jun 13, 2009 at 10:26 AM, Stephan
Friedrichs<deduktionstheorem at web.de> wrote:
> Jochem Berndsen wrote:
>> Keith Sheppard wrote:
>>> Is there any reason that sum isn't strict? I can't think of any case
>>> where that is a good thing.
>>>
>>> Prelude> sum [0 .. 1000000]
>>> *** Exception: stack overflow
>>
>> It is useful if the (+) is nonstrict; although I cannot think of any
>> useful mathematical structure where (+) would be nonstrict.
>
> What about some numeric representations?
>
> type MyNum = [()]
>
> instance Num MyNum where
>  (+) = (++)
>
> Regards,
> Stephan
>
> --
>
> Früher hieß es ja: Ich denke, also bin ich.
> Heute weiß man: Es geht auch so.
>
>  - Dieter Nuhr
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-- 
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