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module Main where
import Data.Char (toLower, toUpper)
import Data.Foldable (forM_)
import Data.List (intercalate)
main :: IO ()
main = do
forM_ [One .. Nine] $ putStrLn . fourIsMagic
data Digit
= One
| Two
| Three
| Four
| Five
| Six
| Seven
| Eight
| Nine
deriving (Show, Eq, Ord, Enum)
toCardinal :: Digit -> String
toCardinal = lcFirst . show
fourIsMagic :: Digit -> String
fourIsMagic x = ucFirst $ intercalate ", " $ reverse $ go [] x
where
go acc Four = (toCardinal Four ++ " is magic.") : acc
go acc x =
let cardinal = toCardinal x
next = toEnum (length cardinal - 1)
in go ((cardinal ++ " is " ++ toCardinal next) : acc) next
lcFirst :: String -> String
lcFirst [] = []
lcFirst (x : xs) = toLower x : xs
ucFirst :: String -> String
ucFirst [] = []
ucFirst (x : xs) = toUpper x : xs
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