growing a recursion

.swift

import Foundation

struct Recursion {
    static func generated()
        -> ((() -> Void)?) -> ()
    {
        var tasks: [(() -> ())?] = []
        
        let closure = { (task: (() -> Void)?) in
            tasks.append(task)
            tasks.forEach { $0?() }
        }
        
        return closure
    }
}

let recur = Recursion.generated()

recur { print("1") }
recur { print("2") }
recur { print("3") }
recur { print("4") }

// `1`
// 1, `2`
// 1, 2, `3`
// 1, 2, 3, `4`