Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
learning about Haskell type classes
import qualified Data.Map as Map
-- A tuple of three Ints
type RGB = (Int, Int, Int)
-- Colors can be specified in three ways.
data Color =
ColorName String |
ColorHex String |
ColorRgb Int Int Int
-- This will be used convert from names to RGB values.
colorNameToRgbMap :: Map.Map String RGB
colorNameToRgbMap = Map.fromList [
("red", (255, 0, 0)),
("green", (0, 255, 0)),
("blue", (0, 0, 255))]
-- A Wagon is one kind of thing that has a color.
data Wagon = Wagon {
length :: Int,
width :: Int,
color :: Color
}
-- This type class specifies the function signatures
-- for functions that should be implemented
-- for everything that has a color.
class HasColor a where
getColorName :: a -> String
getColorHex :: a -> String
getColorRgb :: a -> RGB
-- This implements the HasColor type class for the Wagon type.
instance HasColor Wagon where
-- How can these deal with all three ways of defining a color?
getColorName wagon = "some color name"
getColorHex wagon = "some hex value"
getColorRgb wagon = (1, 2, 3)
main :: IO ()
main = do
let wagon = Wagon 36 20 (ColorName "red")
let name = getColorName wagon
putStrLn $ "name = " ++ name
let hex = getColorHex wagon
putStrLn $ "hex = " ++ hex
let rgb = getColorRgb wagon
putStrLn $ "rgb = " ++ show rgb
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment