package main

import "fmt"

type Any interface{}
type FuncType func(Any, Any) Any
type ConsType func(FuncType) Any

func Cons(a, b Any) ConsType {
	return func(fn FuncType) Any {
		return fn(a, b)
	}
}
func Car(cons ConsType) Any {
	head := func(a, b Any) Any { return a }
	return cons(head)
}

func Cdr(cons ConsType) Any {
	tail := func(a, b Any) Any { return b }
	return cons(tail)
}


/*
 foldl :: (a -> b -> a) -> a -> [b] -> a
 foldl f z []     = z
 foldl f z (x:xs) = foldl f (f z x) xs
*/
func foldl(fn FuncType, init Any, list ConsType) Any {
     if list == nil {
          return  init
     }
     head,tail := Car(list),Cdr(list)
     rest,_ := tail.(ConsType)

     return foldl(fn, (fn(init, head)), rest)
}

/*
 foldr :: (a -> b -> b) -> b -> [a] -> b
 foldr f z []     = z
 foldr f z (x:xs) = f x (foldr f z xs)
*/
func foldr(fn FuncType, fini Any, list ConsType) Any {
    if list == nil {
       return fini
    }

    head, tail := Car(list), Cdr(list)
    rest,_ := tail.(ConsType)
    return fn(head, foldr(fn, fini, rest))
}

func walkDownList(list ConsType) {
	var printer func(a, b Any) Any
	printer = func(a, b Any) Any {
		fmt.Println(a)
		if b == nil {
			fmt.Println('m')
			return nil
		}
		if bVal, castOk := b.(ConsType); castOk {
			bVal(printer)
		}
		return nil
	}
	list(printer)
}
func main() {
	fmt.Println("Hello, playground")
	a := Cons(12, 13)
	print2 := func(x,y Any) Any { return fmt.Sprintf("(%v,%v)",x,y) }
	add2:= func(x, y Any) Any {
	fmt.Println("...", x,y)
	return x.(int) + y.(int)
	 }
	fmt.Println(a(add2))
	list := Cons(12, Cons(14, Cons(16, nil)))
	fmt.Println(list, '!')
	walkDownList(list)
	fmt.Println("..",foldl(add2, 0, list))
	fmt.Println("!!",foldr(add2, 0, list))

	fmt.Println("..",foldl(print2, 0, list))
	fmt.Println("!!",foldr(print2, 0, list))
}