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Today's Topics:
1. Re: any feedback on this solution (Roelof Wobben)
2. Re: any feedback on this solution (Chadda? Fouch?)
3. Re: any feedback on this solution (Chadda? Fouch?)
4. ODP: Re: any feedback on this solution (Marek Wawrzyczek)
----------------------------------------------------------------------
Message: 1
Date: Sat, 07 Feb 2015 17:01:28 +0100
From: Roelof Wobben <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] any feedback on this solution
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Message: 2
Date: Sat, 7 Feb 2015 17:06:02 +0100
From: Chadda? Fouch? <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] any feedback on this solution
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You should probably not remove toDigitsRev, especially since it's normally
a piece of the correct solution for sumDigits... Your current sumDigits is
incorrect, try it on [100, 100].
On Sat, Feb 7, 2015 at 5:01 PM, Roelof Wobben <[email protected]> wrote:
> Oke,
>
> toDigitsRev was one of the steps of this exercise. but I can remove it.
>
> Roelof
>
>
> Joel Williamson schreef op 7-2-2015 om 16:56:
>
> Roelof,
>
> It doesn't look like you ever call toDigitsRev. To keep the solution
> clearer, you should remove any unneeded definitions.
>
> Joel
>
>
--
Jeda?
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Message: 3
Date: Sat, 7 Feb 2015 17:11:53 +0100
From: Chadda? Fouch? <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] any feedback on this solution
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On the other hand it will work here since the source is a list of digits
which have been doubled every two elements...
On Sat, Feb 7, 2015 at 5:06 PM, Chadda? Fouch? <[email protected]>
wrote:
> You should probably not remove toDigitsRev, especially since it's normally
> a piece of the correct solution for sumDigits... Your current sumDigits is
> incorrect, try it on [100, 100].
>
> On Sat, Feb 7, 2015 at 5:01 PM, Roelof Wobben <[email protected]> wrote:
>
>> Oke,
>>
>> toDigitsRev was one of the steps of this exercise. but I can remove it.
>>
>> Roelof
>>
>>
>> Joel Williamson schreef op 7-2-2015 om 16:56:
>>
>> Roelof,
>>
>> It doesn't look like you ever call toDigitsRev. To keep the solution
>> clearer, you should remove any unneeded definitions.
>>
>> Joel
>>
>>
> --
> Jeda?
>
>
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Message: 4
Date: Sun, 08 Feb 2015 12:11:18 +0100
From: Marek Wawrzyczek <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] ODP: Re: any feedback on this solution
Message-ID: <[email protected]>
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Wys?ane z telefonu Samsung
-------- Oryginalna wiadomo?? --------
Od: Roelof Wobben <[email protected]>
Data: 07.02.2015 17:01 (GMT+01:00)
Do: The Haskell-Beginners Mailing List - Discussion of primarily beginner-level
topics related to Haskell <[email protected]>
Temat: Re: [Haskell-beginners] any feedback on this solution
Oke,
toDigitsRev was one of the steps of this exercise. but I can remove it.
Roelof
Joel Williamson schreef op 7-2-2015 om 16:56:
Roelof,
It doesn't look like you ever call toDigitsRev. To keep the solution
clearer, you should remove any unneeded definitions.
Joel
On Sat, 7 Feb 2015 07:50?Kees Bleijenberg <[email protected]> wrote:
Roelof,
Say, you find after a few months a bug or a better algorithm for toDigits,
then you have to remember that sumDigits uses this algorithm (in a bit
different form) too. In this case the functions are so small that it is not
a problem.
If you apply toDigits to all elements of a list of int's and you get almost
the solution
apply toDigits to alle elements of [4,12,3] and you get
[[4],[1,2],[3]],
which is a small step to [4,1,2,3]
Kees
-----Oorspronkelijk bericht-----
Van: Beginners [mailto:[email protected]] Namens Roelof
Wobben
Verzonden: zaterdag 7 februari 2015 11:02
Aan: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell
Onderwerp: Re: [Haskell-beginners] any feedback on this solution
Why,
They have opposite terms.
SumDigits takes a array and has a integer as output.
ToDigits takes a integer and puts out a array.
Roelof
Kees Bleijenberg schreef op 7-2-2015 om 10:56:
> Roelof,
>
> Maybe it's better to reuse toDigits in sumDigits.
>
> Kees
>
> -----Oorspronkelijk bericht-----
> Van: Beginners [mailto:[email protected]] Namens Roelof
> Wobben
> Verzonden: zaterdag 7 februari 2015 10:37
> Aan: The Haskell-Beginners Mailing List - Discussion of primarily
> beginner-level topics related to Haskell
> Onderwerp: [Haskell-beginners] any feedback on this solution
>
> Hello,
>
> I finally solved exercise 1 where I had to write a programm which
> checks if a creditcard number is valid.
>
> I solved it this way :
>
> toDigits :: Integer -> [Integer]
> toDigits n
> | n < 0 = []
> | n < 10 = [n]
> | otherwise = toDigits (n `div` 10) ++ [n `mod` 10]
>
> -- | convert a number to a reversed array where a negative number will
> be a empty array toDigitsRev :: Integer -> [Integer] toDigitsRev 0 =
> [0] toDigitsRev n
> | n < 0 = []
> | n < 10 = [n]
> | otherwise = n `mod` 10 : toDigitsRev (n `div` 10)
>
> -- | Doubles every second number from the right.
> doubleEveryOther :: [Integer] -> [Integer]
> doubleEveryOther [] = []
> doubleEveryOther (x:[])? ? ?= [x]
> doubleEveryOther (x:(y:zs))
> | length (x:(y:zs)) `mod` 2 /= 0 = [x] ++ (y * 2) : doubleEveryOther
zs
> | otherwise = [x *2]? ++ y : doubleEveryOther zs
>
>
> -- | sum all the digits of a array
> sumDigits :: [Integer] -> Integer
> sumDigits [] = 0
> sumDigits (x:zs)
> | x < 10 = x + sumDigits zs
> | otherwise = x `mod` 10 + x `div` 10 + sumDigits zs
>
>
> -- | validate a number by looking if a number can be divided by 10
> validate :: Integer -> Bool validate n =
> sumDigits(doubleEveryOther(toDigits(n))) `mod` 10 == 0
>
>
> -- | The main entry point.
> main :: IO ()
> main = do
> print $ validate 4012888888881881
>
> Any remarks about this solution.
>
> I know there are higher function solutions but that part is not
> descrived in chapter 1 .
>
> Roelof
>
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