https://github.com/ufirstgroup/ymlr

Valid JSON is valid YAML. Any conforming YAML parser should be able to parse JSON. So if you don’t have any specific needs for the YAML format, doing something like:

"---\n" <> Poison.encode!(data)

will produce something any YAML parser will be able to process.

@50kudos For what it’s worth, I found myself in a similar situation. I could parse YAML with yaml-elixir but didn’t have a way to write. So I wrote a short YAML writer myself.

def to_yaml(yaml_map, indentation \\ "") do
    yaml_map
    |> Map.keys
    |> Enum.map(
      fn key ->
        value = Map.fetch!(yaml_map, key)
        cond do
          is_bitstring(value) -> "#{indentation}#{key}: #{value}"
          is_number(value) -> "#{indentation}#{key}: #{value}"
          is_map(value) -> "#{indentation}#{key}:\n#{to_yaml(value, "#{indentation}  ")}"
        end
      end
    )
    |> Enum.join("\n")
end

You use it as follows:

YamlElixir.read_from_file!("file.yaml")
|> Map.put(:some_key, %{some_nested_key: 123})
|> to_yaml

It’s not perfect but it suits my purposes (reading and writing the app.yaml configuration file in Google App Engine).

Thought I’d share to help others who come here while searching, like I did!