Grokdown: Markdown to Ruby Objects

Grokdown provides an experimental interface for building value objects and composing them into entities from a Markdown document tree.

Include the Grokdown module into ruby classes you want Grokdown::Document to consider building value objects from.

Grokdown::Document depends on class methods matches_node? and agruments_from_node to select which Grokdown class to build and how to build an instance from a Markdown node.

Grokdown instances can compose Grokdown value objects or entities by implementing instance hook methods following a naming convention. The hook method name is add_ prefixing the snake case Grokdown class name of the instances a Grokdown instance can get added.

Implementing the hook methods creates precise and resilient factories for objects from Markdown documents.

Simple differences in implementations of add_ composition methods enables building useful ruby object graphs from easy to write Markdown files.

Create a .grokdown file which defines types to build from markdown nodes, then use the grokdown CLI to extract the license name with:

grokdown -e "Document.new(File.read('README.md')).first.license.name"

# Example Readme

Simple readme with a conventional `## License` section

## License

The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).

require "grokdown"

class Text < String
  include Grokdown

  def self.matches_node?(node) = node.type == :text

  def self.arguments_from_node(node) = node.string_content
end

Link = Struct.new(:href, :title, :text, :parent, keyword_init: true) do
  include Grokdown

  def self.matches_node?(node) = node.type == :link

  def self.arguments_from_node(node) = {href: node.url, title: node.title}

  def add_text(node)
    return if text

    self.text = node

    parent.add_composable(node) if parent&.can_compose?(node)
  end
end

License = Struct.new(:text, :href, :name, :link, keyword_init: true) do
  include Grokdown

  def self.matches_node?(node) = node.type == :header && node.header_level == 2 && node.first_child.string_content == "License"

  def add_text(node) = self.text = node

  extend Forwardable

  def_delegator :link, :href

  def add_link(node)
    node.parent = self
    self.link = node
  end

  def add_text(node) = self.name = node
end

Struct.new(:text, :link, :keyword_init) do
  include Grokdown

  def self.matches_node?(node) = node.type == :header && node.header_level == 2

  def add_text(node) = self.text = node
  def add_link(node) = self.link = node
end

Readme = Struct.new(:license) do
  include Grokdown

  def self.matches_node?(node) = node.type == :document

  def add_license(node) = self.license = node
end

Install the gem and add to the application's Gemfile by executing:

$ bundle add grokdown

If bundler is not being used to manage dependencies, install the gem by executing:

$ gem install grokdown

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/cpb/grokdown. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

The gem is available as open source under the terms of the MIT License.

Everyone interacting in the Grokdown project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.