Plotter - simple function plotting

plotter.hs

{-# LANGUAGE DeriveTraversable, GADTs #-}

import Data.List (intersperse,intercalate,transpose)
import Text.Printf (printf)

type Graph = GraphF Bool
type Function = Integer -> Integer -> Bool

height, width :: Integer
height = 40
width = 60

uni, diff :: Function -> Function -> Function
uni f g = \x y -> f x y || g x y
diff f g = \x y -> f x y && not (g x y)

mrAnts, four, foour, foo5 :: Function
four x y = x == 4
foour x y = y == 4
foo5 x y = y^2 + x^2 <= 100
mrAnts = (\x y -> x^2 <= y) `uni` (\x y -> (round . negate $ (1/4 * (fromIntegral x)^2)) + 9 == y)

render :: Bool -> Char
render True = '#'
render False = toEnum 183 

newtype GraphF a = Graph {unGraph :: [[a]]} deriving (Eq,Functor)
instance (a ~ Bool) => Show (GraphF a) where
  show = ("\n "++) . intersperse ' ' . intercalate "\n"
    . (++(map (printf ('%' : show (width + 4) ++ "s") :: String -> String) . transpose . map (printf "%3d") $ range width))
    . map (uncurry (++)) . zip (reverse . map (printf "%3d") $ range height) . unGraph . fmap render

range :: Integral a => a -> [a]
range p = [negate (p`div`2)..(p`div`2)]

genGraph :: Integral a => a -> a -> GraphF (a,a)
genGraph width height = Graph . flip map (reverse $ range height) . traverse (,) $ range width

plot :: Function -> Graph 
plot f = fmap (uncurry f) (genGraph width height)