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Today's Topics:
1. How is takeWhile implemented? (Carlos J. G. Duarte)
2. Re: How is takeWhile implemented? (illusionoflife)
3. Re: How is takeWhile implemented? (Carlos J. G. Duarte)
4. Re: How is takeWhile implemented? (KC)
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Message: 1
Date: Mon, 09 Jul 2012 18:01:49 +0100
From: "Carlos J. G. Duarte" <[email protected]>
Subject: [Haskell-beginners] How is takeWhile implemented?
To: [email protected]
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Message: 2
Date: Mon, 09 Jul 2012 21:18:54 +0400
From: illusionoflife <[email protected]>
Subject: Re: [Haskell-beginners] How is takeWhile implemented?
To: [email protected]
Message-ID: <1898327.KjfVtskrWR@miracle>
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On Monday, July 09, 2012 18:01:49 Carlos J. G. Duarte wrote:
> underK k (x:xs) = (if x < k then [x] else []) ++ underK k xs
>
> -- from [2] ... how does this work anyway?
> fibs = 0 : 1 : zipWith (+) fibs (tail fibs)
> Which seems to work ok. How is takeWhile stopping at a given point and my
> underK not?
Look. In your implementation `underK' you *always* call itself.
So, actually you implemented filter. takeWhile can be implemented(you can
easily see source
http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-List.html.
Take notion that takeWhile do not call itself anymore if predicate is false.
> Other question is regarding the "$" and ".". I know the $ has lower priority
> and . has more, but is there any more difference that matters, I mean, can
> I always use the "$" everywhere. For example, this main also works: main =
> putStrLn $ show $ sum $ filter even $ takeWhile (<_M) fibs
> Is it doing the same thing?
It only affect amount of parensisis. Point is nice for high-order function
magic.
--
Best regards, illusionoflife.
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Message: 3
Date: Mon, 09 Jul 2012 21:30:40 +0100
From: "Carlos J. G. Duarte" <[email protected]>
Subject: Re: [Haskell-beginners] How is takeWhile implemented?
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Message: 4
Date: Mon, 9 Jul 2012 14:26:44 -0700
From: KC <[email protected]>
Subject: Re: [Haskell-beginners] How is takeWhile implemented?
To: "Carlos J. G. Duarte" <[email protected]>,
[email protected]
Message-ID:
<CAMLKXy=PypLQ_AFRU1cFSU98ro1Yt0LAvanm=pzyq0yhl17...@mail.gmail.com>
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Then think of another approach to doing the problem. :)
On Mon, Jul 9, 2012 at 1:30 PM, Carlos J. G. Duarte <
[email protected]> wrote:
>
> Thanks, that's it. I had just to move the underK call inside the if:
>
> underK k (x:xs) = if x < k then x : underK k xs else []
>
> ... I'm finding this to be a little too awkward to me!
>
>
>
--
--
Regards,
KC
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