Why my list function eats memory? - comp.lang.haskell

Допис з розмови Why my list function eats memory?

Ertugrul Söylemez

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Більше налаштувань 29 Вер 2008, 00:14

Групи новин: comp.lang.haskell

Від: Ertugrul Söylemez <e...@ertes.de>

Дата: Sun, 28 Sep 2008 23:14:46 +0200

Локально: Пн 29 Вер 2008 00:14

Тема: Re: Why my list function eats memory?

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Paul Graphov <grap...@gmail.com> wrote:
> Wow, I's much prettier code than my...

> But I don't understand it a bit...

> "iterate (drop d)" produces a list of infinite tails.

> "map (take n)" takes their prefixes.

> But what "takeWhile(not . null)" does in case of infinite input list?
> There should be no null tails.

The 'iterate' function never stops iterating. Its result is, by
definition, an infinite list. This is problematic here, because without
the 'takeWhile', 'drop' will happily produce the empty list out of the
empty list infinitely, so you will get an infinite result list all the
time, even if the argument is a finite list.

> If I try to remove "takeWhile(not . null)" the function works the same
> way if i need only a few windows but if i try to get millionth one it
> causes stack overflow again. The original version works fine.
> How that takeWhile helps?

Honestly I have no idea. This may be a compiler or interpreter issue.
It works without problems for me (GHC 6.8.3), even in interpreter mode.

Greets,
Ertugrul.

--
nightmare = unsafePerformIO (getWrongWife >>= sex)

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