import Data.List;

closest :: [(Float, Float)] -> Float
closest l = closest' $ sortBy (\a b -> (compare  (fst a) (fst b))) l
    where
    closest' []  = 10.0**30.0;
    closest' [a] = 10.0**30.0;
    closest' [a,b]  = dist a b
    closest' s =
        let h   = splitAt ((length s) `div` 2) s
            d1  = closest' (fst h)
            d2  = closest' (snd h)
            md  = min  d1 d2
            xp  = fst $ head $ (snd h)
            t   = sortBy  (\a b -> (compare (snd a) (snd b))) [x | x<-s, (abs  ((fst x)-xp)) < md]
            d3  = comp6 t
        in (min md d3)
        where
            comp6 []     = 10.0**30.0;
            comp6 (x:xs) = min (comp6' x (take 6 xs)) (comp6 xs)
                where
                    comp6' p [] = 10.0**30.0;
                    comp6' p (x:xs) = (min (dist p x) (comp6' p xs))

dist a b = sqrt  ( ((fst a) - (fst b))**2.0 + ((snd a) - (snd b))**2.0)