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

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

> Enum.fold has to set up an exception stack every time it calls next.  It
> only catches an exception once- but it has to set up the stack frame every
> single time.  And that costs.

You're benchmark is just comparing one try...catch with one None/Some
matching. When you are doing some O(1) functional operations you have to do
1 try...catch and 'N' None/Some matching. But according to your results I
modified the implementation of fold in order not to setup a stack frame
every time :

let fold f init t =
 let acc = ref init in
 let rec loop() =
  acc := f (t.next()) !acc;
  loop()
 in
 try
  loop()
 with
  No_more_elements -> !acc

It should now be very efficient.

> In either case, interface harmonization is a more important issue IMHO.
> The exported definition of next should not be any more complicated than:
>     let next t = t.next ()

I already told several times about this : if we let escape the
No_more_elements exception outside of the API, then maybe one iter upper in
the call stack will catch it and break iteration , so if the user fail to
catch it properly when calling next() it can cause very error prone
behaviors since he won't be noticed about the exception being raised.

exemple  :

let e1 = List.enum [1;2;3]
let e2 = List.enum []

let combine x =
    (x  , Enum.next e2)

let l = Enum.of_list (Enum.map combine e1)

=> []

So we have to keep the current next implementation.

Nicolas Cannasse