>>434-435
lazyに考えれば、もっとシンプルに書けるんじゃね(´･ω･`)？

let rec fix (f : Lazy<_>) = f.Force() (lazy fix f)

let fact = fix <| lazy fun f x -> if x = 0 then 1 else x * f.Force() (x - 1)

do fact 5 |> printfn "%d"