Library for colours

Simple thing for working on colours in the RGB colours space. (The intention being that each component is in the interval 0 ≤ x ≤ 1.) You could just use tuples, but this library provides simple colour arithmetic.

module Colour where

data Colour = Colour {red, green, blue :: Double} deriving (Eq, Show)

cmap :: (Double -> Double) -> Colour -> Colour
cmap f (Colour r g b) = Colour (f r) (f g) (f b)

czip :: (Double -> Double -> Double) -> Colour -> Colour -> Colour
czip f (Colour r1 g1 b1) (Colour r2 g2 b2) = Colour (f r1 r2) (f g1 g2) (f b1 b2)

cfold :: (Double -> Double -> Double) -> Colour -> Double
cfold f (Colour r g b) = r `f` g `f` b

cpromote :: Double -> Colour
cpromote x = Colour x x x

instance Num Colour where
  (+) = czip (+)
  (-) = czip (-)
  (*) = czip (*)
  negate = cmap negate
  abs    = cmap abs
  signum = cmap signum
  fromInteger x = cpromote (fromInteger x)

instance Fractional Colour where
  (/) = czip (/)
  recip = cmap recip
  fromRational x = cpromote (fromRational x)

clip :: (Num n, Ord n) => n -> n
clip n
  | n < 0 = 0
  | n > 1 = 1
  | otherwise = n

cclip :: Colour -> Colour
cclip = cmap clip

quantinize :: Int -> Double -> Int
quantinize scale v = floor (v * (fromIntegral scale))