OCaml Weekly News

Hi everyone, I just made an updated version of the OCaml LLVM since the posted one is pretty out of date. Check it out here: https://github.com/adamrk/llvm-ocaml-tutorial. The main changes are:

• switch build system to dune from ocamlbuild
• switch lexing and parsing to use ocamllex/menhir instead of camlp4
• update to newer LLVM API (version 6.0.0)

There are also a couple outstanding issues that I can't figure out, so if you have any ideas how to fix these it'd be really helpful:

• Menhir is generated files which cause warnings during compilation:

  ocamlc lib/parser__mock.mli.inferred
    File "parser__mock.ml.mock", line 388, characters 9-18:
    Warning 3: deprecated: Not_found
  ocamlopt lib/.kaleidoscope_lib.objs/kaleidoscope_lib__Parser.{cmx,o}
    File "parser.ml", line 161, characters 45-612:
    Warning 9: the following labels are not bound in this record pattern: state
  

  Are there any ways to prevent Menhir from causing these warnings? I'm currently handling it by suppressing the warnings with

  (env
   (dev
    (flags (:standard -warn-error -3-9))))
  

  in the dune file. Alternatively, is there a way to suppress the warnings only for these specific files?

• The cstubs are currently printing to stderr because when I set them to print to stdout, those calls don't occur until the program exists. Any ideas on why that happens and if there is a better fix?
• I'm currently linking the cstubs dynamically which is annoying. Does anyone know if there's a way to statically link them in?

You can locally disable the warnings with [@ocaml.warning “-9”] or [@@ocaml.warning “-9”]. If you use a version of ocaml prior to 4.06, you may be better off by wrapping the module with

[@@@ocaml.warning “-9”]
...
[@@@ocaml.warning “+9”]

Hack_parallel is a standalone parallel and shared memory library based on the components used in FB tools Hack, Flow, and Pyre. The internals of these components are little known outside of these projects, yet stand to benefit the OCaml community more generally, both for practical use and educational purposes. So I extracted the core parts and packaged it up; more information can be found in the project README.

I put together an example project to illustrate the basic interface.

Exciting stuff!

But how seriously should I take these warnings?

https://github.com/rvantonder/hack-parallel/blob/master/src/heap/hh_shared.c

From some more details:

You can ignore the scary THIS CODE ONLY WORKS WITH HACK. The implementation works generally (it's used in Flow/Pyre and my own projects without problems). The warning is overcompensating so that people do not treat it like a "generic atomic hashtable for OCaml". The data structure and constraints on memory operations are explained well here. I may document the points in the video in future, but hope that helps for now.

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Here are links from many OCaml blogs aggregated at OCaml Planet.

• Accelerating Self-Play Learning in Go
• Machining the ultimate hackathon prize