Re: [Ocaml-lib-devel] ExtArray?

[Amit D. <ami...@gm...>]

On 11/24/05, Richard W. M. Jones <ri...@me...> wrote:

> > Actually, I agree it makes complete sense for partition.  As I think
> about
> > it, I think filter and find_all should be different.  find_all should
> return
> > a list, and filter should return an array.  And possibly, filter should
> be
> > defined in terms of find_all.
>
> Perhaps you can share your thinking on this :-)
>

Sorry!

I think the principle of least surprise is going to be that
> Array.filter should return an array - this is surely what users would
> expect.


I agree: filter implies you're given a container,  then you "filter" away
some elements, still left with the same type of container.

Find_all suggests you're just looking for all matching elements.  It doesn'=
t
suggest any particular data structure.  So, a list is as good as anything.

The problem will be in the implementation which may require
> two passes -- it could be solved better if there was a truncation
> primitive for arrays.


As I suggested above, one way to implement filter is just:

let filter x y =3D of_list (find_all x y)

There are a number of other implementations, it might make sense to write a
benchmark to decide which is faster.  One worry with a two-pass approach,
though, is it might be incompatible with find/inclusion functions that
contain state (i.e. the state might get confused on the 2nd call).

-Amit