In this document and related Nix expressions we use the term Beam to describe the environment. Beam is the name of the Erlang Virtial Machine and, as far as we know, from a packaging perspective all languages that run on Beam are interchangable. The things that do change, like the build system, are transperant to the users of the package. So we make no distinction.

By default Rebar3 wants to manage it's own dependencies. In the normal non-Nix, this is perfectly acceptable. In the Nix world it is not. To support this we have created two versions of rebar3, rebar3 and rebar3-open. The rebar3 version has been patched to remove the ability to download anything from it. If you are not running it a nix-shell or a nix-build then its probably not going to work for you. rebar3-open is the normal, un-modified rebar3. It should work exactly as would any other version of rebar3. Any Erlang package should rely on rebar3 and thats really what you should be using too.

Both Mix and Erlang.mk work exactly as you would expect. There is a bootstrap process that needs to be run for both of them. However, that is supported by the buildMix and buildErlangMk derivations.

Beam packages are not registered in the top level simply because they are not relevant to the vast majority of Nix users. They are installable using the beamPackages attribute set. You can list the avialable packages in the beamPackages with the following command: $ nix-env -f "<nixpkgs>" -qaP -A beamPackages beamPackages.esqlite esqlite-0.2.1 beamPackages.goldrush goldrush-0.1.7 beamPackages.ibrowse ibrowse-4.2.2 beamPackages.jiffy jiffy-0.14.5 beamPackages.lager lager-3.0.2 beamPackages.meck meck-0.8.3 beamPackages.rebar3-pc pc-1.1.0 To install any of those packages into your profile, refer to them by their attribute path (first column): $ nix-env -f "<nixpkgs>" -iA beamPackages.ibrowse The attribute path of any Beam packages corresponds to the name of that particular package in Hex or its OTP Application/Release name.

There is a Nix functional called buildRebar3. We use this function to make a derivation that understands how to build the rebar3 project. For example, the epression we use to build the hex2nix project follows. {stdenv, fetchFromGitHub, buildRebar3, ibrowse, jsx, erlware_commons }: buildRebar3 rec { name = "hex2nix"; version = "0.0.1"; src = fetchFromGitHub { owner = "ericbmerritt"; repo = "hex2nix"; rev = "${version}"; sha256 = "1w7xjidz1l5yjmhlplfx7kphmnpvqm67w99hd2m7kdixwdxq0zqg"; }; beamDeps = [ ibrowse jsx erlware_commons ]; } The only visible difference between this derivation and something like stdenv.mkDerivation is that we have added erlangDeps to the derivation. If you add your Beam dependencies here they will be correctly handled by the system. If your package needs to compile native code via Rebar's port compilation mechenism. You should add compilePort = true; to the derivation.

Erlang.mk functions almost identically to Rebar. The only real difference is that buildErlangMk is called instead of buildRebar3 { buildErlangMk, fetchHex, cowlib, ranch }: buildErlangMk { name = "cowboy"; version = "1.0.4"; src = fetchHex { pkg = "cowboy"; version = "1.0.4"; sha256 = "6a0edee96885fae3a8dd0ac1f333538a42e807db638a9453064ccfdaa6b9fdac"; }; beamDeps = [ cowlib ranch ]; meta = { description = ''Small, fast, modular HTTP server written in Erlang.''; license = stdenv.lib.licenses.isc; homepage = "https://github.com/ninenines/cowboy"; }; }

Mix functions almost identically to Rebar. The only real difference is that buildMix is called instead of buildRebar3 { buildMix, fetchHex, plug, absinthe }: buildMix { name = "absinthe_plug"; version = "1.0.0"; src = fetchHex { pkg = "absinthe_plug"; version = "1.0.0"; sha256 = "08459823fe1fd4f0325a8bf0c937a4520583a5a26d73b193040ab30a1dfc0b33"; }; beamDeps = [ plug absinthe]; meta = { description = ''A plug for Absinthe, an experimental GraphQL toolkit''; license = stdenv.lib.licenses.bsd3; homepage = "https://github.com/CargoSense/absinthe_plug"; }; }

Often, all you want to do is be able to access a valid environment that contains a specific package and its dependencies. we can do that with the env part of a derivation. For example, lets say we want to access an erlang repl with ibrowse loaded up. We could do the following. ~/w/nixpkgs ❯❯❯ nix-shell -A beamPackages.ibrowse.env --run "erl" Erlang/OTP 18 [erts-7.0] [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false] Eshell V7.0 (abort with ^G) 1> m(ibrowse). Module: ibrowse MD5: 3b3e0137d0cbb28070146978a3392945 Compiled: January 10 2016, 23:34 Object file: /nix/store/g1rlf65rdgjs4abbyj4grp37ry7ywivj-ibrowse-4.2.2/lib/erlang/lib/ibrowse-4.2.2/ebin/ibrowse.beam Compiler options: [{outdir,"/tmp/nix-build-ibrowse-4.2.2.drv-0/hex-source-ibrowse-4.2.2/_build/default/lib/ibrowse/ebin"}, debug_info,debug_info,nowarn_shadow_vars, warn_unused_import,warn_unused_vars,warnings_as_errors, {i,"/tmp/nix-build-ibrowse-4.2.2.drv-0/hex-source-ibrowse-4.2.2/_build/default/lib/ibrowse/include"}] Exports: add_config/1 send_req_direct/7 all_trace_off/0 set_dest/3 code_change/3 set_max_attempts/3 get_config_value/1 set_max_pipeline_size/3 get_config_value/2 set_max_sessions/3 get_metrics/0 show_dest_status/0 get_metrics/2 show_dest_status/1 handle_call/3 show_dest_status/2 handle_cast/2 spawn_link_worker_process/1 handle_info/2 spawn_link_worker_process/2 init/1 spawn_worker_process/1 module_info/0 spawn_worker_process/2 module_info/1 start/0 rescan_config/0 start_link/0 rescan_config/1 stop/0 send_req/3 stop_worker_process/1 send_req/4 stream_close/1 send_req/5 stream_next/1 send_req/6 terminate/2 send_req_direct/4 trace_off/0 send_req_direct/5 trace_off/2 send_req_direct/6 trace_on/0 trace_on/2 ok 2> Notice the -A beamPackages.ibrowse.env.That is the key to this functionality.

Getting access to an environment often isn't enough to do real development. Many times we need to create a shell.nix file and do our development inside of the environment specified by that file. This file looks a lot like the packaging described above. The main difference is that src points to project root and we call the package directly. { pkgs ? import "<nixpkgs"> {} }: with pkgs; let f = { buildRebar3, ibrowse, jsx, erlware_commons }: buildRebar3 { name = "hex2nix"; version = "0.1.0"; src = ./.; erlangDeps = [ ibrowse jsx erlware_commons ]; }; drv = beamPackages.callPackage f {}; in drv

We can leveral the support of the Derivation, regardless of which build Derivation is called by calling the commands themselv.s # ============================================================================= # Variables # ============================================================================= NIX_TEMPLATES := "$(CURDIR)/nix-templates" TARGET := "$(PREFIX)" PROJECT_NAME := thorndyke NIXPKGS=../nixpkgs NIX_PATH=nixpkgs=$(NIXPKGS) NIX_SHELL=nix-shell -I "$(NIX_PATH)" --pure # ============================================================================= # Rules # ============================================================================= .PHONY= all test clean repl shell build test analyze configure install \ test-nix-install publish plt analyze all: build guard-%: @ if [ "${${*}}" == "" ]; then \ echo "Environment variable $* not set"; \ exit 1; \ fi clean: rm -rf _build rm -rf .cache repl: $(NIX_SHELL) --run "iex -pa './_build/prod/lib/*/ebin'" shell: $(NIX_SHELL) configure: $(NIX_SHELL) --command 'eval "$$configurePhase"' build: configure $(NIX_SHELL) --command 'eval "$$buildPhase"' install: $(NIX_SHELL) --command 'eval "$$installPhase"' test: $(NIX_SHELL) --command 'mix test --no-start --no-deps-check' plt: $(NIX_SHELL) --run "mix dialyzer.plt --no-deps-check" analyze: build plt $(NIX_SHELL) --run "mix dialyzer --no-compile" If you add the shell.nix as described and user rebar as follows things should simply work. Aside from the test, plt, and analyze the talks work just fine for all of the build Derivations.

Updating the Hex packages requires the use of the hex2nix tool. Given the path to the Erlang modules (usually pkgs/development/erlang-modules). It will happily dump a file called hex-packages.nix. That file will contain all the packages that use a recognized build system in Hex. However, it can't know whether or not all those packages are buildable. To make life easier for our users, it makes good sense to go ahead and attempt to build all those packages and remove the ones that don't build. To do that, simply run the command (in the root of your nixpkgs repository). that follows. $ nix-build -A beamPackages That will build every package in beamPackages. Then you can go through and manually remove the ones that fail. Hopefully, someone will improve hex2nix in the future to automate that.