Хвостовая рекурсия F# с XAMARIN MAC OS

Я пытаюсь реализовать этот пример из http://fsharpforfunandprofit.com/posts/recursive-types-and-folds-2/

Я использую Xamarin 6.1.5 для MAC OS.

Вот код

type Book = {title: string; price: decimal}

type ChocolateType = Dark | Milk | SeventyPercent
type Chocolate = {chocType: ChocolateType ; price: decimal}

type WrappingPaperStyle = 
    | HappyBirthday
    | HappyHolidays
    | SolidColor

type Gift =
    | Book of Book
    | Chocolate of Chocolate 
    | Wrapped of Gift * WrappingPaperStyle
    | Boxed of Gift 
    | WithACard of Gift * message:string

// A Book
let wolfHall = {title="Wolf Hall"; price=20m}
// A Chocolate
let yummyChoc = {chocType=SeventyPercent; price=5m}
// A Gift
let birthdayPresent = WithACard (Wrapped (Book wolfHall, HappyBirthday), "Happy Birthday")
// A Gift
let christmasPresent = Wrapped (Boxed (Chocolate yummyChoc), HappyHolidays)

let rec cataGift fBook fChocolate fWrapped fBox fCard gift :'r =
    let recurse = cataGift fBook fChocolate fWrapped fBox fCard
    match gift with 
    | Book book -> 
        fBook book
    | Chocolate choc -> 
        fChocolate choc
    | Wrapped (gift,style) -> 
        fWrapped (recurse gift,style)
    | Boxed gift -> 
        fBox (recurse gift)
    | WithACard (gift,message) -> 
        fCard (recurse gift,message) 

let totalCostUsingCata gift =
    let fBook (book:Book) = 
        book.price
    let fChocolate (choc:Chocolate) = 
        choc.price
    let fWrapped  (innerCost,style) = 
        innerCost + 0.5m
    let fBox innerCost = 
        innerCost + 1.0m
    let fCard (innerCost,message) = 
        innerCost + 2.0m
    // call the catamorphism
    cataGift fBook fChocolate fWrapped fBox fCard gift

let deeplyNestedBox depth =
    let rec loop depth boxSoFar =
        match depth with
        | 0 -> boxSoFar 
        | n -> loop (n-1) (Boxed boxSoFar)
    loop depth (Book wolfHall)


let rec totalCostUsingAcc costSoFar gift =
    match gift with 
    | Book book -> 
        costSoFar + book.price  // final result
    | Chocolate choc -> 
        costSoFar + choc.price  // final result
    | Wrapped (innerGift,style) -> 
        let newCostSoFar = costSoFar + 0.5m
        totalCostUsingAcc newCostSoFar innerGift 
    | Boxed innerGift -> 
        let newCostSoFar = costSoFar + 1.0m
        totalCostUsingAcc newCostSoFar innerGift 
    | WithACard (innerGift,message) -> 
        let newCostSoFar = costSoFar + 2.0m
        totalCostUsingAcc newCostSoFar innerGift 


let rec foldGift fBook fChocolate fWrapped fBox fCard acc gift :'r =
    let recurse = foldGift fBook fChocolate fWrapped fBox fCard 
    match gift with 
    | Book book -> 
        let finalAcc = fBook acc book
        finalAcc     // final result
    | Chocolate choc -> 
        let finalAcc = fChocolate acc choc
        finalAcc     // final result
    | Wrapped (innerGift,style) -> 
        let newAcc = fWrapped acc style
        recurse newAcc innerGift 
    | Boxed innerGift -> 
        let newAcc = fBox acc 
        recurse newAcc innerGift 
    | WithACard (innerGift,message) -> 
        let newAcc = fCard acc message 
        recurse newAcc innerGift


let totalCostUsingFold gift =  

    let fBook costSoFar (book:Book) = 
        costSoFar + book.price
    let fChocolate costSoFar (choc:Chocolate) = 
        costSoFar + choc.price
    let fWrapped costSoFar style = 
        costSoFar + 0.5m
    let fBox costSoFar = 
        costSoFar + 1.0m
    let fCard costSoFar message = 
        costSoFar + 2.0m

    // initial accumulator
    let initialAcc = 0m

    // call the fold
    foldGift fBook fChocolate fWrapped fBox fCard initialAcc gift 


[<EntryPoint>]
let main args =

       printfn "Arguments passed to function : %A" args
       let a = deeplyNestedBox 100000

       let res2= a |> totalCostUsingFold 


       // printfn "res2 = %A" res2
       0

Мне кажется, что это хвостовая рекурсия (как сказано на веб-странице), но я получаю ошибку stackoverflow во время выполнения

В параметрах компиляции проекта я выбрал поле «генерировать хвостовые вызовы».

Что-то не так с моим кодом или с Xamarin?