open System.Diagnostics

let n = 1000000
let a = Array.init n id

let measure f s =
    let sw = new Stopwatch();
    sw.Start()
    let r = f()
    sw.Stop()
    printfn s r (sw.Elapsed)
    ()

let test reader =
    Seq.fold (fun acc i -> if i % 2 = 0 then acc + reader i else acc - reader i) 0 { 0 .. n - 1 }

measure (fun () -> test (fun i -> a.[i])) "read1: %A [%O]"
measure (fun () -> test (Array.get a)) "read2: %A [%O]"