How can I use a user inputted value in my Function in F#

Question

I'm trying to make a simple factorial function in F# that uses a value inputted from the user (using the console, I don't know if that makes any difference) but I can't seem to find any solution to be able to use the value from the user in my function.

    open System

    let rec fact x =
        if x < 1 then 1
        else x * fact (x - 1)

    let input = Console.ReadLine()
    Console.WriteLine(fact input)

It constantly gives me the error saying "This expression was expected to have type "int" but here has type "string"". If anyone has any idea on how to make it work properly (or at least can tell me what I need to do to convert my user inputted value into an INT, that would be greatly appreciated.

Answer 1

F# does no automatic conversions for you, so you'll need to parse the string:

open System

let rec fact x =
    if x < 1 then 1
    else x * fact (x - 1)

let input = Console.ReadLine()
Console.WriteLine(fact (Int32.Parse input))

In theory you would need to convert back to string to print it, but it works because there is an overload for Console.WriteLine that takes an integer and does the conversion.