Check out the example app elm-todomvc. In brief:

• Add an app.json file
  • Ensure that a second buildpack provides the web server (elm-todomvc uses the static buildpack)
• Specify the value of ELM_COMPILE (command used to compile your Elm sources) in app.json
• Add the elm buildpack: heroku buildpacks:add https://github.com/srid/heroku-buildpack-elm
  • Add static buildpack if needed: heroku buildpacks:add https://github.com/hone/heroku-buildpack-static
• Deploy!
  • e.g. git commit -am "empty" && git push heroku master && heroku ps:scale web=1

The buildpack aims to use the latest version of Elm by default. To specify an alternative Elm version, create this file in your repo:

$ cat .buildpack.env
export ELM_VERSION=0.15
^D

By default, this buildpack will save and reuse intermediate build objects between deploys. If you want to perform a clean build on every deploy, you may specify that in your .buildpack.env file:

$ cat .buildpack.env
export CACHE_BUILD_OBJECTS=false
^D

Binaries are generated using docker, and uploaded to s3.

# To generate docker image containing the binaries
make binaries

# To upload to s3
aws configure  # creates ~/.aws/...
make upload

• Modify the ELM_VERSION env var in Dockerfile
• make binaries upload
• Modify the ELM_VERSION env var in bin/compile
• Update CHANGELOG.md
• git push

Feel free to ask in Github Issues.