Measure time of execution in F#

Question

Please post code for displaying time in F#. I noticed that you can measure it from F# interactive with #time directive, but I don\'t know how to execute program from FSI

Answer 1

I would just use the .NET Stopwatch class.

let stopWatch = System.Diagnostics.Stopwatch.StartNew()
...
stopWatch.Stop()
printfn "%f" stopWatch.Elapsed.TotalMilliseconds

Answer 2

You could also create custom computation expression to hide actual measuring logic, e.g.:

timer {
   // your code goes here
}

See more examples here: https://fsharpforfunandprofit.com/posts/computation-expressions-bind/

Answer 3

Check out the timer function in the F Sharp Programming wikibook. It is defined like this:

let duration f = 
    let timer = new System.Diagnostics.Stopwatch()
    timer.Start()
    let returnValue = f()
    printfn "Elapsed Time: %i" timer.ElapsedMilliseconds
    returnValue    

Whilst being used like this:

let sample() = System.Threading.Thread.Sleep(2)

duration ( fun() -> sample() )
// or
duration sample

Answer 4

From msdn:

By itself, #time toggles whether to display performance information. When it is enabled, F# Interactive measures real time, CPU time, and garbage collection information for each section of code that is interpreted and executed.

So to test you function you have to open F# interactive console and execute your function in it (one way to do it is to select your function, right click and chose Execute in Interactive) Then make a call to your function in Interactive like that for example:

// define your function first either in interactive console or in your document:

let square x = x * x

// in interactive
#time
square 10
#time

You will see how much of real time and CPU time were spent on computation and a bit of information from garbage collector