[Haskell-cafe] curious about sum

[Deniz Dogan]

2009/6/13 Jochem Berndsen <jochem at functor.nl>:
> 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.

I remember needing a non-strict sum at least once, but I do not
remember the exact application. But imagine having a (very) long list
of numbers and you want to do A if the sum exceeds a small number,
otherwise B.

if sum [0..100000] > 10 then A else B

However, this idea didn't work, because of strictness.

-- 
Deniz Dogan