Require sexplib < v0.9.0

[talex5]

Otherwise, building fails on OCaml 4.03 and 4.04 with:

# File "./make_includes.ml", line 1:
# Error: Reference to undefined global `Ephemeron'
# *** omake: targets were not rebuilt because of errors:
#    src/compiler/includes.ml
#       depends on: src/compiler/make_includes.ml
#       depends on: src/runtime/common-inc.ml
#       depends on: src/runtime/reader-inc.ml
#       depends on: src/runtime/builder-inc.ml

See also: #16

[avsm]

This is actually due to a bug in OCaml 4.04.0 (that was missing Ephemereon from the standard include list). My understanding is that 4.04.1 should fix this, so perhaps we should just make this library require the latest OCaml -- that fits in with its use of flambda anyway, that requires a fairly modern compiler.

[talex5]

flambda works with 4.02. I don't know if anyone is using this library with 4.02 or 4.03. It seems a shame to drop them just to support a newer sexplib (a library which we don't appear to be using anyway).

[avsm]

There have been significant improvements/changes in flambda between 4.03 and 4.04. You may be able to get away with conflicting with just 4.04.0 and allowing 4.03.0 to install.

[talex5]

Dropping < 4.04.1 affects everyone using the library though, not just people who care about the flambda optimisations. Wouldn't it make more sense for the broken versions of sexplib to have the constraint?

[avsm]

That's true -- the challenge is just figuring out where to put the constraint.

Although, it occurs to me that this is a non-issue if #24 is merged, since jbuilder seems to just work correctly with ppx_driver in all the versions of OCaml. Have you tried relaxing the constraint on sexplib with #24?

[talex5]

#24 breaks the optmisations on all versions of OCaml, due to https://caml.inria.fr/mantis/view.php?id=7538

[talex5]

It seems that only the top-level is broken. With the removal of camlp4, we don't need to run the make-includes.ml script anyway.

[talex5]

I tried making a version of the no-camlp4 branch without this patch, but it then breaks for other reasons when used with modern versions of core_kernel. So I'm going to merge this now, then merge the camlp4 work, then upgrade to a more recent core/base to get rid of it again.