[Haskell-cafe] how to break foldl' ?

[Thomas Davie]

Again, it depends how takeWhile is implemented -- if it's not tail  
recursive, the compiler will usually manage to run such functions in  
constant space.

Bob

On 30 Sep 2005, at 16:02, gary ng wrote:

> Once again, many thanks to all who taught me about
> this small little problem. Don't even know there is
> init/last and thought there is only head/tail.
>
> But just for my curiosity, would the takeWhile still
> store the intermediate result till my result is
> reached ? If so, and my list is really very long(and I
> need to go to 1/2 of its length), I would still use a
> lot more memory than imperative method or even the
> foldl one(where in both case, I just take one element)
> ?
>
> --- Henning Thielemann <lemming at henning-thielemann.de>
> wrote:
>
>
>> No problem:
>>   last (takeWhile (<maxX) (scanl (+) 0 xs))
>>     Convinced?
>>
>> The first sum which exceeds the limit could be
>> computed with
>>   head (dropWhile (<=maxX) (scanl (+) 0 xs))
>>
>>
>>
>
>
>
>
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