Skip to content

Yaml parser for Elixir based on native Erlang implementation


Notifications You must be signed in to change notification settings


Folders and files

Last commit message
Last commit date

Latest commit


Repository files navigation

YAML Parser for Elixir

Build Status Module Version Hex Docs Total Download License Last Updated

This is a wrapper for yamerl - a native Erlang YAML parser which brings all of the functionalities to Elixir language.


Add :yaml_elixir as a dependency in your mix.exs file.

defp deps do
     # ...
    {:yaml_elixir, "~> x.x"},

Where x.x.x equals the version in mix.exs (you can omit the last x). Always make sure to use the latest version.

Once you've done that, run mix deps.get in your command line to fetch the dependency.


With YamlElixir you have an access to two functionalities: one for parsing a string and an another one for parsing a file.

Run iex -S mix in your terminal to try how their works.

Parsing a string

yaml = """
  a: a
  b: 1
  c: true
  d: ~
  e: nil
"  a: a\n  b: 1\n  c: true\n  d: ~\n  e: nil\n"
{:ok, %{"a" => "a", "b" => 1, "c" => true, "d" => nil, "e" => "nil"}}

Parsing a file

path = Path.join(File.cwd!(), "test/fixtures/flat.yml")
{:ok, %{"a" => "a", "b" => 1, "c" => true, "d" => nil, "e" => []}}

Support for atoms

By default, all map keys are processed as strings, as are all bareword or quoted values.

If you prefer to autodetect keys and values that begin with : as atoms, this can be accomplished by passing atoms: true as an option to any of the read_* functions.

yaml = """
  a: a
  b: 1
  c: true
  d: ~
  e: nil
  :f: :atom
"  a: a\n  b: 1\n  c: true\n  d: ~\n  e: nil\n"
YamlElixir.read_from_string(yaml, atoms: true)
{:ok, %{:f => :atom, "a" => "a", "b" => 1, "c" => true, "d" => nil, "e" => "nil"}}

Atoms are not garbage collected by BEAM, so be careful with this option, and don't use it with user-supplied input.

If you enable autodetection of atoms, any string values entered (e.g. ":not_really_an_atom") will be converted to atoms, as well. If you only need to support a few atom values, it might be better to enable yamerl's custom tag for atoms:

:yamerl_app.set_param(:node_mods, [:yamerl_node_erlang_atom])

and then using the somewhat inconvenient syntax for it:

atom_key: !<tag:yamerl,2012:atom> atom_value

Support for keyword lists

Keyword lists can be returned in two ways. Either all maps can be transformed into keyword lists via the option maps_as_keywords: true or individually with a tag. To mark a block as a keyword list you must first pass in the node module which can process the tokens:

:yamerl_app.set_param(:node_mods, [YamlElixir.Node.KeywordList])

and then tag the desired block:

  foo: !<tag:yaml_elixir,2019:keyword_list>
    foo: bar
    bar: foo

This will return:

%{"prod" => %{"foo" => [{"bar", "foo"}, {"foo", "bar"}]}}

Note that due to a quirk in how yamerl parses YAML documents, using the flow style with this tag will not work. Do not expect your document to be processed if you write your YAML like this:

  foo: !<tag:yaml_elixir,2019:keyword_list> {foo: bar, bar: foo}

Elixir Sigil

The YamlElixir.Sigil module provides the ~y sigil that can be useful for example for keeping short configurations or other inlined YAML.

import YamlElixir.Sigil

@config ~y"""
debug: false
port: 9200
  - some/file.csv
  - another/file.csv

Use the a sigil modifier to turn on atom values from YAML:

~y":answer: yes"a

You can find more examples in test directory.

Merging anchors

In case your YAML contains anchors, you can have these resolved by passing merge_anchors: true:

yaml = """
  foo: &foo
    bar: 42
    <<: *foo
"  foo: &foo\n    bar: 42\n  baz:\n    <<: *foo\n"
YamlElixir.read_from_string(yaml, merge_anchors: true)

will result in

%{"yaml" => %{"foo" => %{"bar" => 42}, "baz" => %{"bar" => 42}}}

Mix tasks

Sometimes, you may want to use yaml_elixir in your mix tasks. To do that, you must ensure that the application has started.


After that, you will be able to use :yaml-elixir in your mix tasks.


In case of any problems or suggestions do not hesitate and create a pull request.


Copyright and License

Copyright (c) 2022 Kamil Lelonek

This library is MIT licensed. See the LICENSE for details.