Calculate Roman numerals with F#

gistfile1.fs

module RomanNumerals

// Define function
let convertToRoman n =

    let steps = [
        (1, 3, "I")
        (4, 4, "IV") 
        (5, 8, "V")
        (9, 9, "IX") 
        (10, 39, "X")
        (40, 49, "XL")
        (50, 89, "L")
        (90, 99, "XC")
        (100, 399, "C")
        (400, 499, "CD")
        (500, 899, "D")
        (900, 999, "CM")
        (1000, 3999, "M") ]

    let isWithin n (low, high) =
        low <= n && n <= high

    let getStep n = 
        try
            steps
            |> List.find (fun (low, high, step) -> isWithin n (low, high)) 
            |> Some
        with
            | _ -> None

    let rec createRoman n accumulator =
        match getStep n with
        | Some(low, high, step) -> createRoman (n - low) (accumulator + step)
        | None -> accumulator

    createRoman n ""

// Run program
printfn "Enter a number between 1 and 3999:"

System.Console.ReadLine()
    |> int32
    |> convertToRoman
    |> printfn "%s"

printfn "Press any key to exit..."

System.Console.ReadKey() 
    |> ignore