PureScript by Example - 5.14 Record Puns - Exercise 1-3 Solutions

RecordPuns.purs

module RecordPuns where

import Prelude
import Data.Maybe

-- Utilities provided in 5.12 Algebraic Data Types of PureScript by Example
data Shape
  = Circle Point Number
  | Rectangle Point Number Number
  | Line Point Point
  | Text Point String
data Point = Point
  { x :: Number
  , y :: Number
  }

-- Exercise 1
myShape :: Shape
myShape = Circle (Point { x: 0.0, y: 0.0 }) 10.0

-- Exercise 2
doubleSize :: Shape -> Shape
doubleSize (Circle (Point { x, y }) r) =
  Circle (Point { x: 2.0 * x, y: 2.0 * y }) (2.0 * r)
doubleSize (Rectangle (Point { x, y }) l w) =
  Rectangle (Point { x: 2.0 * x, y: 2.0 * y }) (2.0 * l) (2.0 * w)
doubleSize (Line (Point { x: x1, y: y1 }) (Point { x: x2, y: y2 })) =
  Line (Point { x: 2.0 * x1, y: 2.0 * y1 }) (Point { x: 2.0 * x2, y: 2.0 * y2 })
doubleSize (Text (Point { x, y }) s) =
  Text (Point { x: 2.0 * x, y: 2.0 * y }) s

-- Exercise 3
textFromShape :: Shape -> Maybe String
textFromShape (Text _ s) = Just s
textFromShape _ = Nothing