#light// define an exception typeexception WrongSecond of int// list of prime numberslet primes =    [ 2; 3; 5; 7; 11; 13; 17; 19; 23; 29; 31; 37; 41; 43; 47; 53; 59 ]// function to test if current second is primelet testSecond() =    try        let currentSecond = System.DateTime.Now.Second in        // test if current second is in the list of primes        if List.exists (fun x -> x = currentSecond) primes then        // use the failwith function to raise an exception            failwith "A prime second"        else            // raise the WrongSecond exception            raise (WrongSecond currentSecond)        with            // catch the wrong second exception            WrongSecond x ->                printf "The current was %i, which is not prime" x    // call the functiontestSecond()

#light// function to write to a filelet writeToFile() =// open a file    let file = System.IO.File.CreateText("test.txt")    try    // write to it    file.WriteLine("Hello F# users")    finally    // close the file, this will happen even if    // an exception occurs writing to the file    file.Dispose()// call the functionwriteToFile()