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{-# LANGUAGE OverloadedLists, TypeFamilies #-}
import qualified Data.Set as S
import GHC.Exts
main = do putStrLn (f [])
putStrLn (f [1,2])
putStrLn (f [2,0])
putStrLn (f [3,2])
putStrLn (f [2,7])
putStrLn (f [2,2])
putStrLn (f [1..7])
f :: S.Set Int -> String
f [] = "empty"
f [_] = "one element"
f [2,_] = "two elements, the smaller one is 2"
f [_,2] = "two elements, the bigger one is 2"
f _ = "else"
instance Ord a => IsList (S.Set a) where
type (Item (S.Set a)) = a
fromList = S.fromList
toList = S.toList
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