F#: Converting a string into an array of bytes

Question

I'm writing a simple rc4 encryption/decryption utility as a first project. I'm stuck on trying to convert the given string into an array of bytes that can then be manipulated by the core algorithm. How do you convert a string into an array of bytes in functional f#?

//From another thread
let private replace find (repl : string) (str : string) = str.Replace(find, repl)

//let private algorithm bytes = blah blah blah

let Encrypt (decrypted : string) =
    decrypted.Chars
    |> Array.map(fun c -> byte.Parse(c)) // This line is clearly not working
    // |> algorithm
    |> BitConverter.ToString
    |> replace "-" ""

FYI in C# it looks like:

    public static string Encrypt(string decrypted)
    {
        byte[] bytes = new byte[decrypted.Length];

        for (int i = 0; i < decrypted.Length; ++i)
            bytes[i] = (byte)decrypted[i];

        Algorithm(ref bytes);

        return BitConverter.ToString(bytes).Replace("-", "").ToLower();
    }

Answer 1

Although you could write your own function to do the job, its best to stick with the built-in .NET methods:

String to bytes:

System.Text.Encoding.ASCII.GetBytes("hello world!")

Bytes to string:

System.Text.Encoding.ASCII.GetString([|104uy; 101uy; 108uy; 108uy;
            111uy; 32uy; 119uy; 111uy; 114uy; 108uy; 100uy; 33uy|])