Trampolines in F#

trampoline.fsx

let trampoline f c n =
    let rec loop = function
    | Choice1Of2 x -> x
    | Choice2Of2 x -> loop (f x)
    loop (Choice2Of2 (c,n))

// Test
let factorial n = 
    let rec factorialT (current, n) =
        if n = bigint 0 then Choice1Of2 current
        else Choice2Of2 (current * n, n - 1I)
    trampoline factorialT 1I n

factorial 20000I