[Haskell] specification of sum

Sebastian Sylvan sebastian.sylvan at gmail.com
Tue Nov 1 17:41:46 EST 2005

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

Sebastian Sylvan
UIN: 44640862

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