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Today's Topics:
1. Simplified Luhn Algorithm (trent shipley)
2. Re: Simplified Luhn Algorithm (mrx)
----------------------------------------------------------------------
Message: 1
Date: Sun, 31 Dec 2017 04:01:51 +0000
From: trent shipley <trent.ship...@gmail.com>
To: Haskell Beginners <beginners@haskell.org>
Subject: [Haskell-beginners] Simplified Luhn Algorithm
Message-ID:
<caeflybl-2cjwasnzfr3sn7u2+-fkwhuwfxzfezm4mpqwb3v...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
I have the following, and it works, but I am trying teach myself Haskell,
and I have the suspicion that my solutions is both inefficient and
graceless. Any feedback would be appreciated.
Trent.
------------------------------------
{-
8.The Luhn algorithm is used to check bank card numbers for simple errors
such as mistyping a digit, and proceeds as follows:
* consider each digit as a separate number;
* moving left, double every other number from the second last;
* subtract 9 from each number that is now greater than 9;
* add all the resulting numbers together;
* if the total is divisible by 10, the card number is valid.
Define a function luhnDouble :: Int -> Int that doubles a digit
and subtracts 9 if the result is greater than 9.
For example:
> luhnDouble 3
6
> luhnDouble 6
3
Using luhnDouble and the integer remainder function mod, define a function
luhn :: Int -> Int -> Int -> Int -> Bool
that decides if a four-digit bank card number is valid.
For example:
> luhn 1 7 8 4
True
> luhn 4 7 8 3
False
In the exercises for chapter 7 we will consider a more general version of
this function that accepts card numbers of any length.
Hutton, Graham. Programming in Haskell (pp. 45-46). Cambridge University
Press. Kindle Edition.
-}
luhnDouble :: Int -> Int
luhnDouble x = if (2 * x) > 9
then (2 * x) - 9
else 2 * x
luhn :: Int -> Int -> Int -> Int -> Bool
luhn x1 x2 x3 x4 = if 0 == sum[luhnDouble x1, x2, luhnDouble x3, x4] `mod`
10
then True
else False
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Message: 2
Date: Sun, 31 Dec 2017 09:49:12 +0100
From: mrx <patrik....@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Simplified Luhn Algorithm
Message-ID:
<canzojbgn7yhymcwbozb5stm4-eik1orcbteu2rzhurqcd-g...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
I guess your issue is how to represent the card numbers of arbitrary
length, or? Wouldn't a list work?
Patrik
Den 31 dec 2017 05:03 skrev "trent shipley" <trent.ship...@gmail.com>:
I have the following, and it works, but I am trying teach myself Haskell,
and I have the suspicion that my solutions is both inefficient and
graceless. Any feedback would be appreciated.
Trent.
------------------------------------
{-
8.The Luhn algorithm is used to check bank card numbers for simple errors
such as mistyping a digit, and proceeds as follows:
* consider each digit as a separate number;
* moving left, double every other number from the second last;
* subtract 9 from each number that is now greater than 9;
* add all the resulting numbers together;
* if the total is divisible by 10, the card number is valid.
Define a function luhnDouble :: Int -> Int that doubles a digit
and subtracts 9 if the result is greater than 9.
For example:
> luhnDouble 3
6
> luhnDouble 6
3
Using luhnDouble and the integer remainder function mod, define a function
luhn :: Int -> Int -> Int -> Int -> Bool
that decides if a four-digit bank card number is valid.
For example:
> luhn 1 7 8 4
True
> luhn 4 7 8 3
False
In the exercises for chapter 7 we will consider a more general version of
this function that accepts card numbers of any length.
Hutton, Graham. Programming in Haskell (pp. 45-46). Cambridge University
Press. Kindle Edition.
-}
luhnDouble :: Int -> Int
luhnDouble x = if (2 * x) > 9
then (2 * x) - 9
else 2 * x
luhn :: Int -> Int -> Int -> Int -> Bool
luhn x1 x2 x3 x4 = if 0 == sum[luhnDouble x1, x2, luhnDouble x3, x4] `mod`
10
then True
else False
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