Re: [Ocaml-lib-devel] Enum.has_next (was : More thoughts on Enum)

[Nicolas C. <war...@fr...>]

>     let default_has_next next count =
>         let lookahead = ref None in
>         let has_next' () =
>             match lookahead with
>                 Some x -> true
>                 | None -> try
>                     lookahead := Some (next ());
>                     true
>                     with No_more_elements -> false
>         and next' () =
>             match lookahead with
>                 Some x ->
>                     lookahead := None;
>                     x
>                 | None ->
>                     next()
>         and count' () ->
>             match lookahead with
>                 Some _ -> 1 + (count ())
>                 | None -> count()

This is a little more complicated than that...
Actually calling count() can make next being called ( if this is a count
calling force ), and then the return of count() will be the total number of
elements, including the lookhead, so you'll count 1 more element since
you're adding 1. You could first call count and then match again the
lookahead to see if still Some.... but that's pretty inneficient.
You can have a look at current Enum.peek implementation, I think it resolves
the problem in a nice and elegant way.

Nicolas Cannasse