読者です 読者をやめる 読者になる 読者になる

by shigemk2

当面は技術的なことしか書かない

自作のデータ型を自作のモジュールからエクスポートする

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

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))

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

baseRect :: Float -> Float -> Shape
baseRect width height = Rectangle (Point 0 0) (Point width height)
import Shapes
-- main = do
--      print $ Circle (Point 10 20) 30

-- こんなエラーが出るお
-- Main.hs:3:14: Not in scope: data constructor `Circle'
-- Main.hs:3:22: Not in scope: data constructor `Point'

main = do
     print $ nudge (baseCircle 30) 10 20
-- Circle (Point 10.0 20.0) 30.0