Re: [Caml-list] parameterized pattern

[Martin Jambon <martin1977@laposte.net>]

On Mon, 6 Nov 2006, Serge Aleynikov wrote:

> Hi,
>
> The section 6.6 of OCaml's manual introduces a notion of "Parenthesized
> patterns".
>
> I couldn't find any examples on how to use this feature, and brute-force
> approach doesn't work:
>
> # match 1.0 with
>   (y : float)  -> print_float y
> | (s : string) -> print_string s;;
> This pattern matches values of type string
> but is here used to match values of type float
> #
>
> Could anyone point at a suitable resource?

What you wrote is equivalent to:

match ((1.0 : float) : string) with
    y -> print_float y
  | s -> print_string s

In OCaml, match-with is a test against the structure of a value, not its
type. What you want to do is not currently possible in OCaml.


Martin

--
Martin Jambon, PhD
http://martin.jambon.free.fr