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

[Alan P. <ap...@re...>]

In article <Pin...@ea...>, Brian Hurt wrote:
> 
> Sorry, I just had an epiphany on this issue.  With enums we always have a 
> good count, right?  I mean, we're not implementing my "-1 means we don't 
> know how many elements are in the enumeration".
> 
> The enum code should use this and never cause an exception to be thrown.  
> Therefor it doesn't need to catch the exceptions either.
> 
> let iter f e =
>     let c = e.count() in
>     for i = 1 to c do
>         f (e.next())
>     done
> 
> let fold f x e =
>     let rec loop c accu =
>         if c <= 0 then accu
>         else loop (c-1) (f (e.next ()) accu)
>     in
>     loop (e.count ()) x

This undoes the lazy nature of Enum.filter, Enum.filter_map, and even
more seriously, input_enum and input_char_enum.  Basically, anywhere
the code uses Enum.from will be a problem when relying on Enum.count.