These 'nice errors' are available on a forked version of the OCaml compiler. The hope is to merge them back into mainline OCaml, but it will be an uphill battle, I think, to convince the OCaml maintainers to merge them, because they're very conservative about changes (which can be good) and may not appreciate the value of friendly error messages (which is not so good).
I can assure you that the OCaml maintainers do appreciate the value of friendly error messages, despite your drive-by comments about our ethos.
However, unfinished patches cannot be merged into our mainline tree, and this PR https://github.com/ocaml/ocaml/pull/102 needs some attention to rebase it to trunk, and also to get feedback from testers who may have tried the opam switch and have comments.
(associated writeup https://arxiv.org/abs/1512.01897)
Help welcome on this particular patch, and other newer ones from Reason that can be ported over to OCaml and submitted as normal feature improvements.
Sorry avsm. I looked at the patch you linked to and indeed the OCaml developers are all quite enthusiastic about improved error messages. My mistake. The only real blocker is what we both mentioned I believe, that we all want to go slow to make sure the best possible work is merged in.
By the way, the above patch is different from the one that ReasonML uses. Realistically, the work done by the Reason team is more recent and actually shipped with the BuckleScript platform, so now the blocker is, which direction does the OCaml compiler want to go in.
