Moving.hs

Moving.hs

{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances, FlexibleContexts #-}
import Geom2D

left :: (Num a) => Point a -> a -> Point a
left (Point x y) n = Point (x - n) y

right :: (Num a) => Point a -> a -> Point a
right (Point x y) n = Point (x + n) y

up :: (Num a) => Point a -> a -> Point a
up (Point x y) n = Point x (y - n)

down :: (Num a) => Point a -> a -> Point a
down (Point x y) n = Point x (y + n)

class Num n => Moving p n | p -> n where
  up'    :: n -> p -> p
  down'  :: n -> p -> p

  up'    n = down'  (-n)
  down'  n = up'    (-n)

instance Num a => Moving (Point a) a where
  up' n (Point x y) = Point x (y - n)

p = Point 0 0

main = print $ up' 10 p