Memoized.swift

struct Memoized<A: Equatable, R> {
    typealias Value = (_ params: A) -> R
    var callback: Value
    @XState private var prevParam: A? = nil
    @XState private var prevValue: R? = nil

    init(_ callback: @escaping Value) {
        self.callback = callback
    }
    
    func call(_ param: A) -> R {
        defer {
            self.prevParam = param
        }
        
        if self.prevParam != param {
            self.prevValue = callback(param)
        }
        
        return self.prevValue!
    }
}