let inline (|Parse|_|) (str: string): ^a option =
    let mutable value = Unchecked.defaultof< ^a>
    let result = (^a: (static member TryParse: string * byref< ^a> -> bool) str, &value)
    if result then Some value
    else None
   
let foobar str =
    match str with
    | Parse(x: int) -> "int"
    | Parse(x: float) -> "float"
    | Parse(x: System.Guid) -> "guid"
    | _ -> "other"
    
printfn "%s" (foobar "42")