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  1. import Control.Applicative
  2. import Control.Monad (guard)
  3. import Control.Arrow 
  4. import Data.List (unfoldr)
  5.  
  6. g = sum   . filter even
  7.           . unfoldr ( runKleisli (returnA &&& Kleisli (\x ->
  8.                    x`div`2 <$ guard(even x)
  9.                <|> x*3 + 1 <$ guard( x/=1 )
  10.              )))
  11.  
  12. main = print $ g 201
Success #stdin #stdout 0s 5728KB
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https://ideone.com/eScxaq
language:
Haskell (ghc 8.4.4)
created:
10 years ago
visibility:
secret

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