HackerRank find the perimeter of a polygon from a list of points

perimeter-polygon.hs

-- Enter your code here. Read input from STDIN. Print output to STDOUT
import Control.Monad (forM)

hypot :: Floating a => a -> a -> a -> a -> a
hypot lx ly rx ry = sqrt $ (((rx-lx)**2)+((ry-ly)**2))

-- Fold over a list of points, taking the Euclidean distance, and 
-- rotate the next point between each call until we reach an empty list
fp :: Floating a => a -> [a] -> [[a]] -> a
fp acc (lx:ly:[]) ((rx:ry:[]):t) = fp (acc + (hypot lx ly rx ry)) [rx,ry] t
fp acc (lx:ly:[]) [] = acc

-- Process input from STDIN and output to STDOUT
main :: IO ()
main = do
    n <- getLine -- Number of points changes the forM length
    points <- forM [1..(read n :: Int)] (\a -> do
        lin <- getLine
        return $ map (\x -> read x :: Float) $ words lin)
    -- add the head to the tail to cycle all points (ex: f 0 A [B,C,A])
    putStrLn $ show $ fp 0.0 (head points) $ (tail points)++[(head points)]