Here's a part of it:

        type Shape =
            | Rock
            | Paper
            | Scissors

        let parseCharacters (line: string) =
            let onlySingleCharacters (a: string, b: string) = a.Length = 1 && b.Length = 1

            match line.Split() with
            | [| a; b |] when onlySingleCharacters (a, b) ->
                match a[0], b[0] with
                | 'A', 'X' -> Some(Rock, Rock)
                | 'A', 'Y' -> Some(Rock, Paper)
                | 'A', 'Z' -> Some(Rock, Scissors)
                | 'B', 'X' -> Some(Paper, Rock)
                | 'B', 'Y' -> Some(Paper, Paper)
                | 'B', 'Z' -> Some(Paper, Scissors)
                | 'C', 'X' -> Some(Scissors, Rock)
                | 'C', 'Y' -> Some(Scissors, Paper)
                | 'C', 'Z' -> Some(Scissors, Scissors)
                | _ -> None
            | _ -> None

        let rec readLines () =
            let line = Console.ReadLine()

            match line with
            | null
            | "" -> []
            | _ ->
                match parseCharacters line with
                | Some parsedLine -> parsedLine :: readLines ()
                | None -> readLines ()