Active pattern date matching

activePatternDateMatch.fsx

// I like this active pattern stuff

open System.Globalization

let (|ShortDate|_|) s =
    match DateTime.TryParseExact(s, "ddMMMyyyy", CultureInfo.InvariantCulture, DateTimeStyles.None) with
    | true, d -> Some d
    | _ -> None

let (|LongDate|_|) s =
    match DateTime.TryParseExact(s, "ddMMMyyyy:HH:mm:ss.fff", CultureInfo.InvariantCulture, DateTimeStyles.None) with
    | true, d -> Some d
    | _ -> None

let parseDate s =
    match s with
    | ShortDate d -> Some d
    | LongDate  d -> Some d
    | _ -> None