January 2017 1HaskellADay 1Liners

• January 31st, 2017:
  You have d = "3.461497957769017000D+07"
  define parseDouble :: String -> Double
  (n.b.: (read d) :: Double throws an error)
• bazzargh @bazzargh uncurry (*) (bimap read ((10^).read.(dropWhile(`elem`"0+D"))) (break (=='D') d))::Double
• January 31st, 2017: Given
  e :: FilePath -> [String] -> [Epoch]
  
  readEpochs :: FilePath -> IO [Epoch]
  readEpochs f = e f . lines <$> readFile f
  
  point-free-itize readEpochs
• Astynax Pirogov @alex_pir uncurry fmap . (((. lines) . e) &&& readFile
• January 30th, 2017: Given
  
  parseNum :: String -> Maybe (Float, String)
  
  define: dropNum'' :: String -> Maybe String
  
  points-free in terms of parseNum
• matt @themattchan dropNum" = fmap snd . parseNum
• January 30th, 2017: For
  
  parseHeader :: String -> Maybe String
  parseHeader str = match "Start " str <|> match "Finish " str
  
  eliminate redundancies
• mconcat . ([match] <*> ["Start ", "Finish "] <*>) . pure
• Nickolay Kudasov @crazy_fizruk If you're allowed to use Monoid instead of Alternative, how about this version?
  foldMap match ["Start", "Finish"]
• Andreas Källberg @Anka213  My solution was
  parseHeader str = foldr1 (<|>) . map (`match` str) $ ["Start", "Finish"]
  But that's longer than the original.
• January 25th, 2017:
  given f is type: f :: Int -> a -> Bool
  
  for: g :: a -> Bool
  g = (||) . f 2 <*> f 27
  
  rewrite g using f only once in the definition
• Denis Stoyanov @xgrommx ugly version but
  (liftA2 . liftA2) (||) ($2) ($27) f
• January 19th, 2017:
  import Data.Tree.Merkle
  
  mkleaf :: Show a => a -> Leaf a
  mkleaf = uncurry Leaf . (show . hashDatum &&& id)
  
  redefine using (<*>)
• Denis Stoyanov @xgrommx smth like
  mkleaf = uncurry Leaf . show . (hashDatum <$> (,) <*> id)
  mkleaf = uncurry Leaf . show . (liftA2 (,) hashDatum id)
• January 19th, 2017:
  mkbranch1 :: Leaf a -> Branch a
  mkbranch1 = uncurry Twig . (uncurry childrenHash . (dataHash &&& dataHash) &&& id)
  
  redefine using (<*>)s(?)