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  1. {-# LANGUAGE TupleSections     #-}
  2.  
  3. import Control.Applicative
  4. import Control.Monad (guard)
  5. import Data.List (unfoldr)
  6.  
  7. g = sum 
  8.           . filter even
  9.           . unfoldr ( \x -> fmap(x,) $
  10.                    x`div`2 <$ guard(even x)
  11.                <|> x*3 + 1 <$ guard( x/=1 )
  12.              )
  13.  
  14. main = print $ g 201
Success #stdin #stdout 0s 5724KB
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stdin 
Standard input is empty
stdout 
4088
https://ideone.com/2bi6nK
language:
Haskell (ghc 8.4.4)
created:
13 years ago
visibility:
secret

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