cons car and cdr in swift

cons.swift

typealias LinkedList  = ((Any, Any) -> Any) -> Any
typealias Cons = (Any, Any) -> LinkedList
typealias Result  = (LinkedList) -> Any

let cons: Cons = { (x: Any, y: Any) in
    {
        (z: (Any, Any) -> Any) in z(x, y)
    }
}

let car: Result  = {
     (z: ((Any, Any) -> Any) -> Any) in z {p, q in p}
}

let cdr: Result  = {
     (z: ((Any, Any) -> Any) -> Any) in z {p, q in q}
}

var each: ((Any, (Any) -> ()) -> ())!

each = { (x: Any, thing: (Any) -> ()) -> () in 
  if let x = x as? LinkedList {
    thing(car(x))
    return each(cdr(x), thing)
  } else {
    thing(x)
  }
}

var each: ((Any, (Any) -> ()) -> ())!

 each = { 
  if let x = $0 as? LinkedList {
    $1(car(x))
    each(cdr(x), $1)
  }
  print("we always got here")
    $1($0)
}

each = { guard let x = $0 as? LinkedList else { return $1($0) }
   $1(car(x))
   each(cdr(x), $1)
}


func each(_ x: Any, _ thing: (Any) -> ()) -> () {
  if let x = x as? LinkedList {
    thing(car(x))
    return each(cdr(x), thing)
  } else {
    thing(x)
  }
}

car(cons(1, 2))
print(cdr(cons(1, cons(2, 3))))
print(car(cons(1, cons(2, 3)))) // => 1
print(cons)

each(cons(1, cons(2, 3)), { x in print(x) })

refactored_scheme.swift

import Foundation

typealias LinkedList  = ((Any, Any) -> Any) -> Any
typealias Cons = (Any, Any) -> LinkedList
typealias Result  = (LinkedList) -> Any
var each: ((Any, (Any) -> ()) -> ())!

let cons: Cons = { (x: Any, y: Any) in
    {
        (z: (Any, Any) -> Any) in z(x, y)
    }
}
let car: Result = { $0 {p, q in p} }

let cdr: Result = { $0 {$1} }

 each = { 
  if let x = $0 as? LinkedList {
    $1(car(x))
    return each(cdr(x), $1)
  }
  print("we always got here")
  $1($0)
}

each(cons(1, cons(2, 4)), { print($0) })

somewtf.swift

let external: (() -> Void) -> Void = { _ in () }
func takesTwoFunctions(first: (() -> Void) -> Void, second: (() -> Void) -> Void) {
    first { first {} }       // Error
    second { second {}  }    // Error

    first { second {} }      // Error
    second { first {} }      // Error

    first { external {} }    // OK
    external { first {} }    // OK
}