types.hs

module Shapes 
(
 Point (..),
 Shape (..),
 area,
 nudge,
 baseCircle,
 baseRect
 ) where

main = putStrLn "Hello World"
-- Point类型，表示平面中的点
data Point = Point Float Float deriving (Show)
-- Shape 是类型，它的值为Circle和Rectangle
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))

baseCircle :: Float -> Shape
baseCircle = Circle (Point 0 0)

baseRect :: Float -> Float -> Shape
baseRect width height = Rectangle (Point 0 0) (Point width height)