import Data.Ratio
import Text.Printf (PrintfType, printf)

-- Map a value from the range [a1,a2] to the range [b1,b2].  We don't check
-- for empty ranges.
mapRange
  :: Fractional a
  => (a, a) -> (a, a) -> a -> a
mapRange (a1, a2) (b1, b2) s = b1 + (s - a1) * (b2 - b1) / (a2 - a1)

main :: IO ()
main
-- Perform the mapping over floating point numbers.
 = do
  putStrLn "---------- Floating point ----------"
  mapM_ (\n -> prtD n . mapRange (0, 10) (-1, 0) $ fromIntegral n) [0 .. 10]
  -- Perform the same mapping over exact rationals.
  putStrLn "---------- Rationals ----------"
  mapM_ (\n -> prtR n . mapRange (0, 10) (-1, 0) $ n % 1) [0 .. 10]
  where
    prtD
      :: PrintfType r
      => Integer -> Double -> r
    prtD = printf "%2d -> %6.3f\n"
    prtR
      :: PrintfType r
      => Integer -> Rational -> r
    prtR n x = printf "%2d -> %s\n" n (show x)