[Haskell] specification of sum

[Sebastian Sylvan]

On 11/1/05, Scherrer, Chad <Chad.Scherrer at pnl.gov> wrote:
> I was wondering... In my experience, it's worked much better to use
>
> sum' = foldl' (+) 0
>
> than the built-in "sum" function, which leaks memory like crazy for
> large input lists. I'm guessing the built-in definition is
>
> sum = foldr (+) 0
>
> But as far as I know, (+) is always strict, so foldl' seems much more
> natural to me. Is there a case where the build-in definition is
> preferable?

The library definition in ghc actually uses foldl.
It's conceivable that you may not want (+) to be non-strict for
certain data types.
The question then becomes, is there a case where you want _sum_ to be
non-strict?


/S
--
Sebastian Sylvan
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