monads: `core_kernel.rope` no longer exists in v0.16

[bmourad01]

It seems this functionality has been separated into the jane_rope package (which currently depends on base v0.16). Would we need to break compatibility with previous versions (i.e. < v0.16.0) of janestreet libraries to upgrade, or hard stop at v0.15? Perhaps a third option exists?

ping @ivg

[ivg]

Do you mean by a hard stop that we shouldn't support versions below v0.15 or above?

[bmourad01]

By that I mean that one option would be to not support anything above v0.15.

[XVilka]

It's better to support newer Core/Base versions in my opinion, since they will benefit from all the OCaml 5.x multicore and effects work in the future, which would fit BAP quite well for variety of reasons. See also #1561

[greedy]

FWIW it is possible to support both using a disjunctive dependency formula and dune's alternative dependency mechanism.

For example, I checked with

( "core_kernel" {>= "v0.14" & < "v0.16"}
| ("core_kernel" {>= "v0.16" & < "v0.17"} & "jane_rope" {>= "v0.16" & < "v0.17"}) )

in monads.opam.

Then with

(library
  (name monads)
  (public_name monads)
  (wrapped false)
  (preprocess (pps ppx_bap))
  (libraries core_kernel
             (select rope_witness.ml from
                     (core_kernel.rope -> rope_witness.core_kernel.ml)
                     (jane_rope -> rope_witness.jane_rope.ml)))
  (private_modules monads_monad monads_monoid monads_types rope_witness))

in lib/monads/dune I could build the monads library against either core_kernel 0.15 or core_kernel 0.16 + rope 0.16.

The rope_witness.*.ml files don't have any code in them, they just are there to make the dune facility work. I put comments in them so that I could see in the build tree which file was selected for rope_witness.ml.

Not sure if it is really worth the complication though :)