RecursiveClosures

Library to make recursive closures easy in Swift.

Why this Library?

Defining a recursive function in Swift is easy:

func fib(n: Int) {
    return n <= 2 ? 1 : fib(n-1) + fib(n-2)
}
 
println(fib(3)) // 8

But how about defining a recursive closure?

let fib : (Int) -> Int = { n in
   n <= 2 ? 1 : fib(n-1) + fib(n-2)
}

In Swift 3.0 this produces the following error: error: variable used within its own initial value

The following would work, but you have to store the closure as implicitly unwrapped var.

var bla : ((Int) -> Int)!
bla = {(n) in
    n <= 2 ? 1 : bla(n-1) + bla(n-2)
}

bla(5)

With RecursiveClosures you can do the following:

let fib = Recursion<Int, Int> { (n, f) in
   n <= 2 ? 1 : f(n-1) + f(n-2)
}.closure

Requirements

iOS 8, Swift 3.0

Installation

###CocoaPods

pod 'RecursiveClosures' => git: 'https://github.com/riisemichi/RecursiveClosures.git', tag: => '0.0.1'

Carthage

TODO

Copy Class

You can simply copy the class Recursion to your Project.

Usage

Recursion is a generic class which takes two Types. One for parameter type, one for return type. Inside the closure you will have a parameter f, which represents the function itself, that can be called recursively.

// Create Closure
let fib = Recursion<Int, Int> { (n, f) in
   n <= 2 ? 1 : f(n-1) + f(n-2)
}.closure

// Run it
fib(6)

Need multiple parameters or return values? Just use Tuples. Example:

// DIN-A
let a = Recursion<Int, (Int, Int)> { (i, f) -> (Int, Int) in
    if i <= 0 {
        return (1189, 841)
    }
    let (h, w) = f(i-1)
    return (w / 2, h)
}.closure

a(6)

###Cached Recursion CachedRecursion optimizes your closure by caching already calculated values. Your function will only be executed for a parameter if it is not found in the cache.

Just add a .cached before the .closure.

// Create Closure
let fib = Recursion<Int, Int> { (n, f) in
   n <= 2 ? 1 : f(n-1) + f(n-2)
}.cached.closure

// Run it
fib(60) //1548008755920

Using the cached version will even calculate a fibonacci of 60 lightning fast.

EmojiCode

If you like it fancy, you can use the Emoji "🌀" instead of "Recursion" (typealias).

let fib = 🌀<Int, Int> { (n, f) in
   n <= 2 ? 1 : f(n-1) + f(n-2)
}.cached.closure