module ChurchFold

open System


let nil (c:'a->'b->'b) (n:'b) : 'b = n

let cons (x:'a) (xs:('a->'b->'b)->'b->'b) : ('a->'b->'b)->'b->'b =
    fun c n -> c x (xs c n)


let toList (xs:('a->'b->'b)->'b->'b) : 'a list =
    xs (fun x acc -> x :: acc) []


let ofList (ls:'a list) : (('a->'b->'b)->'b->'b) =
    List.foldBack (fun x acc -> cons x acc) ls nil


let foldWithPredicate (churchList:(int->int list->int list)->int list->int list) (f:int->int->int) (p:int->bool) (acc:int) : int =

    let regularList = toList churchList
    

    let rec foldTailRec lst accumulator =
        match lst with
        | [] -> accumulator
        | head :: tail ->
            if p head then
    
                foldTailRec tail (f accumulator head)
            else
    
                foldTailRec tail accumulator
    
    foldTailRec regularList acc

[<EntryPoint>]
let main _ =

    let numbers = ofList [1; 2; 3; 4; 5]
    

    let add x y = x + y
    

    let isEven x = x % 2 = 0
    

    let greaterThan2 x = x > 2
    
    printfn "Исходный список: [1; 2; 3; 4; 5]"
    printfn ""
    

    let sumEven = foldWithPredicate numbers add isEven 0
    printfn "Сумма четных чисел (предикат isEven): %d" sumEven
    

    let sumGreater2 = foldWithPredicate numbers add greaterThan2 0
    printfn "Сумма чисел больше 2 (предикат > 2): %d" sumGreater2
    

    let multiply x y = x * y
    let productEven = foldWithPredicate numbers multiply isEven 1
    printfn "Произведение четных чисел: %d" productEven
    
    printfn ""
    printfn "Демонстрация работы с различными предикатами:"
    

    let isOdd x = x % 2 = 1
    let sumOdd = foldWithPredicate numbers add isOdd 0
    printfn "Сумма нечетных чисел: %d" sumOdd
    
    let isPositive x = x > 0
    let countPositive = foldWithPredicate numbers (fun acc _ -> acc + 1) isPositive 0
    printfn "Количество положительных чисел: %d" countPositive
    
    0