Comments on: Luhn algorithm in F# http://www.fsharp.it/2009/04/15/luhn-algorithm-in-f/ Functional programming on .Net Wed, 18 Aug 2010 12:04:06 +0200 http://wordpress.org/?v=2.8.5 hourly 1 By: Pramod http://www.fsharp.it/2009/04/15/luhn-algorithm-in-f/comment-page-1/#comment-3812 Pramod Sun, 10 May 2009 17:03:37 +0000 http://www.fsharp.it/?p=122#comment-3812 I wrote a similar function in Haskell. However, I used map, zip etc. instead of tail recursion. dblDigit d = if 2*d > 9 then 2*d - 9 else 2*d luhn num =    let digits = map digitToInt (show num)      nDigits = length digits      indices = (map (\d -> (nDigits-1) - d) [0..])      values = zip digits indices      modifiedDigits = map (\(d,i) -> if i `mod` 2 == 1 then dblDigit d else d) values      digitSum = sum modifiedDigits    in digitSum `mod` 10 == 0 Might be a personal prefernece, but isn't this method a little bit cleaner? I wrote a similar function in Haskell. However, I used map, zip etc. instead of tail recursion.

dblDigit d = if 2*d > 9 then 2*d – 9 else 2*d
luhn num =
   let digits = map digitToInt (show num)
     nDigits = length digits
     indices = (map (\d -> (nDigits-1) – d) [0..])
     values = zip digits indices
     modifiedDigits = map (\(d,i) -> if i `mod` 2 == 1 then dblDigit d else d) values
     digitSum = sum modifiedDigits
   in digitSum `mod` 10 == 0

Might be a personal prefernece, but isn’t this method a little bit cleaner?

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