Point-Free or Die: Tacit Programming in Haskell and Beyond

pointfree.hs

{- Point-Free or Die: Tacit Programming in Haskell and Beyond

https://www.youtube.com/watch?v=seVSlKazsNk

g . f = (.) g f x
      = \x -> g (f x)
      = \x -> g $ f x
      = \x -> g . f $ x
      = g . f

aggregate f = sum . map f
aggregate f = (.) sum (map f)
aggregate f = (.) sum $ map f
aggregate f = (.) sum . map $ f
aggregate = \f -> (.) sum . map $ f
aggregate = (.) sum . map
aggregate = (sum .) . map

        (sum .) . map
\f g -> (f   .) . g

-- Eta abstraction
\f g -> (f .) . g
\f g x -> (f .) . g $ x
\f g x -> (f .) $ g x
\f g x -> (f .) (g x)
\f g x -> f . (g x)
\f g x y -> f $ (g x) y
\f g x y -> f (g x y)

-- New combinator: blackbird
f ... g = (f .) . g
        - \x y -> f (g x y)

-- Mastermind game
exactMatches = length . filter id ... zipWith (==)

colorMatches ps qs = sum $ zipWith min (countColors ps) (countColors qs)
colorMatches ps qs = sum $ (zipWith min `on` countColors) ps qs
colorMatches = sum ... zipWith min `on` countColors
-}