Re: [Caml-list] Question

[Damien Doligez <damien.doligez@inria.fr>]

On Monday, December 1, 2003, at 04:41 PM, sebastien FURIC wrote:

> # let test t t' = match t, t' with
>   | ((Toto _ | Titi _), Toto x | Toto x, (Toto _ | Titi _)) when x = 0
> -> "OK"
>   | _ -> "KO";;
> Characters 73-79:
> Warning: this pattern is unused.
>   | ((Toto _ | Titi _), Toto x | Toto x, (Toto _ | Titi _)) when x = 0
> -> "OK"
>                                           ^^^^^^
[...]

>  I was expecting "when" to be right distributive over "|".

That notion doesn't make sense because "when" is not a pattern operator.
If you "distribute" when over |, you get this:

  # let test t t' = match t, t' with
    | ((Toto _ | Titi _), Toto x when x = 0
       | Toto x, (Toto _ | Titi _) when x = 0)
      -> "OK"
    | _ -> "KO";;

which is nonsense, from O'Caml's point of view.

-- Damien

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