Re: [Ocaml-lib-devel] unknown length, user defined enumerations?

[Brian H. <bh...@sp...>]

On Fri, 18 Apr 2003, Nicolas Cannasse wrote:

> BTW, about your "count" problem you HAVE TO return the lines count, because
> for exemple Array.of_enum will require it to create the array before putting
> elements inside. The solution is quite easy to do : when "count" is called
> the first time, you're reading all remaining files and then have to modify
> your Enum.t which will now iter on the builded list. This is almost what the
> "Enum.force" is doing, but I modified its behavior so it can be used this
> way.

This is suboptimal in cases- like Xarray and list- where they don't really 
need the count.  Xarray is a very good example.  Count isn't *needed*, but 
it is handy.

Instead, I'd implement Array.of_enum like:

let rec of_enum enum =
    let c = Enum.count enum in
    if (c < 0) then
        (* Convert the enum to a list, then create the array from the
           list *)
        of_enum (List.enum_of (List.of_enum enum))
    else
        Array.init c (fun _ -> Enum.next enum)
;;

This basically does the same thing your example does- it recreates the 
enum as a list, and then enumerates that.

The only of_enum function I can think of that *needs* a count is 
Array.of_enum.  I can think of a lot of enumerations where I don't know, 
at the start, how many elements are in the enumeration.

Brian