Re: [Ocaml-lib-devel] De-functor-ized Psqueue

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

> You have two types (Enum and Stream) and a clear way to distinguish
> them (whether count always makes sense). If you merge them, you push
> the distinguishing feature to runtime.
>
> Also, it's not clear what the semantics of count on Stream are. Consider
> Stream.of_list; does it do one traversal on creation to take the count?
> Does it do it on the first call to count?  What if it's on a List with
> setcdr?  Should count be treated as an expensive or an inexpensive op?
>
> I think it makes sense to create a stream from an enum, but the opposite
> is not true.  I think we are lucky count is there to remind us.  If you
> agree with this, then the two types should not be unified.

I totally agree with you here.
The only thing that should be mentionned, is that you can always use Enum
instead of Stream, because it's better :
- if the user doesn't need count, then it's better because he still can use
all functionnal ops in Enum , as well as of_enum implementations in several
data structures
- if the user does need count, then Enum is providing the best way of doing
it (that is : actually really "counting" elements, one by one) in an
efficient way (see Enum.force) since only the first call to count will be
costly.

Nicolas Cannasse