Timing of fold-functions in F#

time_fold.fs

let inline fold f a (xs: _ []) =
     let mutable a = a
     for i=0 to xs.Length-1 do
        a <- f a xs.[i]
     a

let afold f a (xs: _ []) =
     let mutable a = a
     for i=0 to xs.Length-1 do
        a <- f a xs.[i]
     a

let time name n x = 
    let sw = System.Diagnostics.Stopwatch.StartNew()
    for i = 0 to n do
        x()
    sw.Stop()
    printfn "Executed %s %i times, took %ims " name n sw.ElapsedMilliseconds


let a = [|0..50000|]

//

time "inline fold" 1000 (fun () -> fold (fun s x -> s + x) 0 a |> ignore<int>)
time "Array.fold fold" 1000 (fun () -> Array.fold (fun s x -> s+x) 0 a |> ignore<int>)
time "fold-fn fold" 1000 (fun () -> afold (fun s x -> s+x) 0 a |> ignore<int>)

    
//Executed inline fold 1000 times, took 15ms 
//Executed Array.fold fold 1000 times, took 70ms 
//Executed fold-fn fold 1000 times, took 666ms