nudge.hs

data Point = Point Float Float deriving (Show)
data Shape = Circle Point Float | Rectangle Point Point deriving (Show)

area :: Shape -> Float
area (Circle _ r) = pi * r ^ 2
area (Rectangle (Point x1 y1) (Point x2 y2))
    = (abs $ x2 - x1) * (abs $ y2 - y1)

nudge :: Shape -> Float -> Float -> Shape
nudge (Circle (Point x y) r) a b = Circle (Point (x+a) (y+b)) r
nudge (Rectangle (Point x1 y1) (Point x2 y2)) a b
    = Rectangle (Point (x1+a) (y1+b)) (Point (x2+a) (y2+b))

-- 指定したサイズの図形を原点に作る補助関数を作って、それから移動させる
baseCircle :: Float -> Shape
baseCircle r = Circle (Point 0 0) r

-- 幅と高さを取って、左下の頂点が原点にある長方形を作る関数
baseRect :: Float -> Float -> Shape
baseRect width height = Rectangle (Point 0 0) (Point width height)

main = do
    print $ area (Rectangle (Point 0 0) (Point 100 100))
    print $ area (Circle (Point 0 0) 24)
    print $ nudge (Circle (Point 34 34) 10) 5 10
    print $ nudge (baseRect 40 100) 60 23