pinvoking rust

fact.cs

using System;
using System.Runtime.InteropServices;

public static class Program
{
    [DllImport("fact.dll")]
    private static extern ulong fact(ulong x);

    public static void Main()
    {
        Console.WriteLine(fact(13));
    }
}

fact.rs

#![crate_type = "lib"]

#[no_mangle]
pub extern fn fact(x: u64) -> u64 {
    match x {
        0 => 1,
        _ => x * fact(x-1),
    }
}

ffi.fs

open System.Runtime.InteropServices

[<DllImport("fact.dll")>]
extern uint64 fact(uint64)

[<EntryPoint>]
let main argv = 
    printfn "%u" <| fact 13UL
    0