Question

I am trying to write something like

let timeit (x:'a->'b) =
    let start = System.DateTime.Now
    x
    let duration = System.DateTime.Now - start
    printfn "time usage = %A" duration.Milliseconds 
    ()

it works for

let matrixtest() =
    let x = vector[1.;2.;4.]
    let y = matrix[[1.;2.;4.;];[3.;4.;9.;]]
    printfn "%A" (y * x)
    ()

but not for

let rec fib x = 
        match x with
        | 0 | 1 -> 1
        | n -> fib (n-1) + fib (n-2)

sa F# is static typed.

Any idea? Thanks.

Answer 1

Even in the matrix case you need to apply the function to a value. Try this:

let timeit f v =
  let start = System.DateTime.Now
  let result = f v
  let duration = System.DateTime.Now - start
  printfn "time usage = %A" duration.Milliseconds 
  result

Aequitarum Custos is right about using the StopWatch class, though.