Parse.fsx

let inline parse str = (^a: (static member Parse: string -> ^a) (str))

let inline tryParse str =
    let mutable value = Unchecked.defaultof<_>
    let result = (^a: (static member TryParse: string * byref< ^a > -> bool) (str, &value))
    result, value

(tryParse "3": bool * int)
(tryParse "2.3": bool * float)
(tryParse "2.3": bool * decimal)
(tryParse "true": bool * bool)
(tryParse "tRUE": bool * bool)

(parse "2": int)
(parse "test": int)
(parse "2.3": float)

let inline (|Parsed|_|) x =
    match tryParse x with
    | true, v -> Some v
    | _ -> None

match "true" with
| Parsed 3 -> "The int 3"
| Parsed x -> sprintf "An int %i" x
| Parsed (x: float) -> "A float"
| Parsed true -> "True"
| Parsed false -> "False"
| x -> sprintf "Some other string %s" x