README.md

HelloLfe

This demonstrates a simple Nerves project that's written in LFE.

LFE-izing a Nerves project

Since LFE is a BEAM language, it works great with Nerves. This example project is a trivial LFE/Nerves project. Since the Nerves tooling uses Elixir, the top level project must use Elixir's mix build tool, but dependencies can use other build tools like rebar3.

The following describes what needed to be done after creating a Nerves project the "normal" Elixir-based way using mix nerves.new <project_name>.

The first step is to add LFE as a dependency in your mix.exs:

    {:lfe, "~> 2.0", compile: "make"},

I've found that it's easiest to have mix build LFE source files. The mix_lfe was so close to working, but I had trouble with it (could have been me struggling along the way). To work around the issue, I copied out the mix compiler from it. That's the code in the lib directory. It would be great if someone could work with the mix_lfe maintainer to split the project up so that the compiler piece can be used separately.

The next step is to update the rel/vm.args. First disable embedded mode since it doesn't seem to work with LFE:

#-mode embedded

Then update the -user option to start the LFE shell:

-user lfe_init

Finally, create a src directory and put your LFE code in there like you would in a normal LFE project.

Building

Building follows the standard Nerves recipe. Here's an example:

export MIX_TARGET=bbb
mix deps.get
mix firmware

And then burn an SD card using mix firmware.burn.

Using

The images pull in the standard nerves_pack infrastructure for bringing up networking and other initialization steps. See the config/config.exs for network parameters and other configuration.

Running

Attach to the console of your board (i.e., RPi3 is HDMI, BBB/RPi0 is USB gadget). You should see prints from the application. Note that the first boot takes quite a bit longer than the rest since it initializes the application's writable filesystem.

To see log messages, run:

(Elixir.RingLogger:next)

Notes

The mix_lfe was so close to working, but I had trouble with it. To work around the issue, I copied out the mix compiler from it. That's the code in lib.