module Main where

import Graphics.Gloss
import Data.List

main :: IO ()
main = display (InWindow "Recaman Sequence" (500, 500) (0, 0)) white draw

draw :: Picture
draw = rotate (-35) $ pictures $ snd $ mapAccumL (addarc) [] (map (\n -> fromIntegral n :: Float) (recaman 65))
  where addarc acc n
          | acc == [] = (acc ++ [n], blank)
          | otherwise = (acc ++ [n], translate (last acc - (last acc - n) / 2) 0  $ rotarc $ arcbetween n (last acc))
          where arcbetween a b = arc (-180) 0 ((b - a)/2)
                rotarc a
                  | even $ length acc = rotate 180 a
                  | odd $ length acc = a

recaman :: Int -> [Int]
recaman l = foldl (next) [] [0..l]
  where next acc n
          | n == 0 = acc ++ [n]
          | last acc - n > 0 && not (last acc - n `elem` acc) = acc ++ [last acc - n]
          | otherwise = acc ++ [last acc + n]