[Haskell-cafe] curious about sum
deniz.a.m.dogan at gmail.com
Sat Jun 13 10:17:57 EDT 2009
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,
if sum [0..100000] > 10 then A else B
However, this idea didn't work, because of strictness.
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