Update for lwt 4.0.0

[ncihnegn]

Using core_kernel.Doubly_linked and lwt_log.

[rgrinberg]

I don't think introducing core_kernel is possible (or even desirable). The breaking change should be towards making the hooks abstract IMO. The other changes are fine.

[ncihnegn]

Is it license issue? Could you please elaborate?

[rgrinberg]

It's a huge dependency that's being acquired for a data structure that's quite easy to implement. In particular, I'm not sure how portable core_kernel is on windows.

Why not just inline some simple implementation into the source and keep it abstract? To prevent issues such as this happening in the future.

[rgrinberg]

Thanks, that's a step in the right direction. A few points:

• Could you split out the Camomile change into its own commit? This is unrelated to updating things to Lwt.

• Could you explain the changes to src/lTerm_windows_stubs.c. Ideally, those should be in their own commit as well. With the message describing the change.

• We shouldn't be squatting the name Lwt_dlist. That name really belongs to the Lwt package, so something like lTerm_dlist.ml is a lot better.

• Do we really need a dlist?

We can see that the callbacks module only after adds on the left of this list. If we're going to make a breaking change, why not make something more future proof:

type switch

type 'a callbacks

val create : unit -> 'a callbacks

val fold_left : ('acc -> 'a -> 'acc) -> 'a callbacks -> 'acc -> 'acc

val register : switch option -> 'a callbacks -> 'a -> unit

val exec_callbacks : ('a -> unit) callbacks -> 'a -> unit

val exec_filters : ('a -> bool) callbacks -> 'a -> bool

It doesn't seem like the add_r is even being used anywhere by the users of lambda-term, so I wonder if we can even implement type 'a callbacks = 'a list ref (but keep things abstract of course).

[ncihnegn]

I don't think it is easy to get away with a singly-linked list. The register registers a callback of remove.

[rgrinberg]

Okay, I see. So we'll have to keep the dlist under the hood.

[ncihnegn]

To fix #60

[ghost]

This PR looks ready. I'm merging it and doing a release since it's blocking opam upgrade.

[ghost]

And thanks for this PR!