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internal final class SpinLock {
    private let lock =  NSLock()
    
    func sync<T>(action: () -> T) -> T {
        lock.lock()
        defer { lock.unlock() }
        return action()
    }
}

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extension String {
	private static let whitespaceRegularExpression = try! NSRegularExpression(pattern: "\\s")

	var escapingWhitespaces: String {
		return String.whitespaceRegularExpression.stringByReplacingMatches(
			in: self,
			range: NSRange(location: 0, length: self.utf16.count),
			withTemplate: "\\\\$0"
		)
	}

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    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        navigationController?.isNavigationBarHidden = false
        navigationController?.navigationBar.alpha = 0
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        if let presentedVC = UIApplication.presentedViewController(), presentedVC != self {
            navigationController?.isNavigationBarHidden = true

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protocol Semigroup {
    // Binary, associative semigroup operation (op)
    func op (_ g: Self) -> Self
}

extension Int : Semigroup {
    func op (_ n: Int) -> Int {
        return self + n
    }
}

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protocol Semigroup {
    // Binary semigroup operation
    // **AXIOM** Should be associative:
    //   a.op(b.op(c)) == (a.op(b)).op(c)
    func op (_ g: Self) -> Self
}

extension Int : Semigroup {
    func op (_ n: Int) -> Int {
        return self + n

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indirect enum List <A> {
    case Nil
    case Cons(
        A,
        List<A>
    )
}

func map <A, B> (_ f: @escaping (A) -> B) -> (List<A>) -> List<B> {
    return { xs in

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import Foundation
import Dispatch
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

precedencegroup Additive {
    associativity: left
}

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import Foundation

typealias JSONDict = [String: Any]

struct Parameter<A> {
    let apiDescription: String
    let parse: (Any) -> A?
}

extension Parameter {

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// http://www.futantan.com/2016/04/14/NSTimer-tips/#more

extension NSTimer {
  private class FTTimerClosureWraper {
    private (set) var timerClosure: () -> ()
    
    init(timerClosure: () -> () ) {
      self.timerClosure = timerClosure
    }
  }

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struct Stock {
    var name = ""
    var id = ""
}

let stock1 = Stock(name: "name", id: "1")
let stock2 = Stock(name: "name", id: "2")
let stock3 = Stock(name: "name", id: "3")
let stock4 = Stock(name: "name", id: "4")
let stock5 = Stock(name: "name", id: "5")