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  1. mapIf :: (Int -> Bool) -> (a -> a) -> [a] -> [a]
  2. mapIf pred f l = map (\(value,index) -> if (pred index) then f value else value) $ zip l [1..]
  3.  
  4. mapEveryN :: Int -> (a -> a) -> [a] -> [a]
  5. mapEveryN n = mapIf (\x -> x `mod` n == 0)
  6.  
  7. main = print $ mapEveryN 3 (*2) [1,1,1,1,1,1,1]
Success #stdin #stdout 0s 4700KB
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Standard input is empty
stdout
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[1,1,2,1,1,2,1]
https://ideone.com/kSQwdE
language:
Haskell (ghc 8.4.4)
created:
9 years ago
visibility:
public

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