dentify whether four sides (given by four integers) can form a square, a rectangle, or neither.

polygon.hs

import Data.List.Split (splitOn)

-- polygons.txt
-- 36 30 36 30
-- 15 15 15 15
-- 46 96 90 100
-- 86 86 86 86
-- 100 200 100 200
-- -100 200 -100 200


data Shape = Polygon | Rectangle | Square deriving Show

data Result = Result {polygons::Int, rectangles::Int, squares:: Int} deriving Show

fn xs = case xs of
          (a:b:c:d:t) -> let allPositive = all (>0) xs
                             isRectangle = a == c && b == d
                             isSquare = isRectangle && a == b
                          in if not allPositive
                                then Polygon
                                else if isSquare then Square
                                else if isRectangle then Rectangle
                                else Polygon
          _ -> Polygon

update :: Shape -> Result -> Result
update s r = case s of
               Rectangle ->  r { rectangles = rectangles r + 1 }
               Square -> r { squares = squares r + 1 }
               Polygon -> r { polygons = polygons r + 1 }

main :: IO ()
main = do
  content <- readFile "polygons.txt"
  let parsed = map  ( map (\x -> read x :: Int) . splitOn " ") $ lines content
  let result = map fn parsed
      -- let r = Result 0 0 0
  let count = foldl (\r s -> update s r) (Result 0 0 0) result
  putStrLn $ show count -- Result {polygons = 2, rectangles = 2, squares = 2}