Functional Programming Example in Swift

BattleShip.swift

import Foundation
import UIKit

typealias Position = CGPoint
typealias Distance = CGFloat

typealias Region = Position -> Bool

func inRange1(target: Position, range: Distance) -> Bool {
  return sqrt(target.x * target.x + target.y * target.y) <= range
}

func circle(radius: Distance) -> Region {
		return { point in
      sqrt(point.x * point.x + point.y + point.y) <= radius
		}
}

func shift(offset: Position, region: Region) -> Region{
		return { point in
      let shiftedPoint = Position(x: point.x - offset.x, y: point.y - offset.y)
      return region(shiftedPoint)
		}
}

func invert(region: Region) -> Region {
  return { point in
    !region(point)
  }
}

func intersection(region1: Region, region2: Region) -> Region {
  return { point in
    region1(point) && region2(point)
  }
}

func union(region1: Region, region2: Region) -> Region {
  return { point in
    region1(point) || region2(point)
  }
}

func difference(region: Region, minusRegion: Region) -> Region {
  return intersection(region, invert(minusRegion))
}

let minimumDistance: Distance = 2.0

func inRange(#ownPosition: Position, #target: Position, #friendly: Position, #range: Distance) -> Bool{
  let rangeRegion = difference(circle(range), circle(minimumDistance))
  let targetRegion = shift(ownPosition, rangeRegion)
  let friendlyRegion = shift(friendly, circle(minimumDistance))
  let resultRegion = difference(targetRegion, friendlyRegion)
  
  return resultRegion(target)
}

inRange(ownPosition: Position(x: 5, y: 5), target: Position(x: 8, y: 8), friendly: Position(x: 1, y: 1), range: 10) // true
inRange(ownPosition: Position(x: 5, y: 5), target: Position(x: 6, y: 6), friendly: Position(x: 1, y: 1), range: 10) // false
inRange(ownPosition: Position(x: 5, y: 5), target: Position(x: 8, y: 8), friendly: Position(x: 7, y: 7), range: 10) // true