[giraj]

I was hoping this post would mention using OCaml with flambda[1] enabled. At least for my work, flambda seems to yield a ~10% speed up when compiling things. Can you get OCaml binaries with flambda enabled through Nix? With opam, I currently have to compile OCaml myself to enable it, as I am not aware of any binaries being distributed.

[1] https://v2.ocaml.org/manual/flambda.html

[ParetoOptimal]

The nix option for it was added in 2017:

https://github.com/NixOS/nixpkgs/pull/32946

If you find it important, I'd encourage opening a PR to ask for flambda to be enabled by default at https://github.com/NixOS/nixpkgs/issues/new/choose.

Especially if the ocaml community typically enables flambda by default these days.

[ingenieroariel]

Seems you would need to first override ocaml and then override the ocaml used in mkOcamlPackages. [1]

  let o = ocaml.override { flambdaSupport = true; }; in
  let oP = ocaml-ng.mkOcamlPackages o (self: super: {}); in
  oP.apron

[1] https://discourse.nixos.org/t/install-ocaml-flambda-compiler...

[giraj]

Okay, thanks! But doesn't this still mean you have to compile ocaml (with flambda) yourself?

[mindslight]

If the derivation has already been written (as GP implies), then compiling something yourself with Nix is essentially just a longer installation process. No downloading tarballs, no keeping track of things in /usr/local, no stow or manually adding things to your path. Nix is essentially a source distribution that pulls common binaries from caches.

[baby]

I actively work on an OCaml project and couldn’t understand anything about what flambda does from its readme

[giraj]

I updated the link to point to the docs, which are more informative. As far as I understand, flambda is an intermediate representation of OCaml which allows for a number of optimisations and better inlining. You can check if you already have flambda enabled by runnning "ocamlopt -config | grep flambda".

If you're using opam then you can test flambda out by creating a new switch

  opam switch create ocaml-flambda ocaml-variants.4.14.1+options ocaml-option-flambda

and then running "opam switch set ocaml-flambda". (You can replace 4.14.1 with your preferred version above.)

[momentoftop]

It's a bunch of optimisation passes, I believe mostly around inlining. Ocaml is historically quite passive on that.