Liquex

A Liquid template parser for Elixir.

Liquid template renderer for Elixir with 100% compatibility with the Liquid gem by Shopify. If you find that this library is not byte for byte equivalent to liquid, please open an issue.

Installation

The package is available in Hex and can be installed by adding liquex to your list of dependencies in mix.exs:

def deps do
  [
    {:liquex, "~> 0.6"}
  ]
end

Documentation can be found at https://hexdocs.pm/liquex.

Basic Usage

iex> {:ok, template_ast} = Liquex.parse("Hello {{ name }}!")

iex> context = Liquex.Context.new(%{"name" => "World"})

iex> {content, _context} = Liquex.render(template_ast, context)

iex> content |> to_string()
"Hello World!"

Supported features

Currently, all standard Liquid tags, filters, and types are fully supported. Liquex can be considered a drop in replacement of the Liquid gem, but in Elixir.

Supported:

Lazy variables

Liquex allows resolver functions for variables that may require some extra work to generate. For example, Shopify has variables for things like available products. Pulling all products every time would be too expensive to do on every render. Instead, it would be better to lazily pull that information as needed.

Instead of adding the product list to the context variable map, you can add a function to the variable map. If a function is accessed in the variable map, it is executed.

products_resolver = fn _parent -> Product.all() end

with context <- Liquex.Context.new(%{products: products_resolver}),
    {:ok, document} <- Liquex.parse("There are {{ products.size }} products"),
    {result, _} <- Liquex.render(document, context) do
  result
end

iex> "There are 5 products"

Indifferent access

By default, Liquex accesses your maps and structs that may have atom or string (or other type) keys. Liquex will try a string key first. If that fails, it will fall back to using an atom keys. This is similar to how Ruby on Rails handles many of its hashes.

This allows you to pass in your structs without having to replace all your keys with string keys.

iex> {:ok, template_ast} = Liquex.parse("Hello {{ name }}!")
iex> context = Liquex.Context.new(%{name: "World"})
iex> {content, _context} = Liquex.render(template_ast, context)
iex> content |> to_string()
"Hello World!"

Custom filters

Liquex contains the full suite of standard Liquid filters, but you may find that there are still filters that you may want to add.

Liquex supports adding your own custom filters to the render pipeline. When creating the context for the renderer, set the filter module to your own module.

defmodule CustomFilter do
  # Import all the standard liquid filters
  use Liquex.Filter

  def scream(value, _), do: String.upcase(value) <> "!"
end

context = Liquex.Context.new(%{}, filter_module: CustomFilter)
{:ok, template_ast} = Liquex.parse("{{'Hello World' | scream}}"

{result, _} = Liquex.render(template_ast, context)
result |> to_string()

iex> "HELLO WORLD!"

Custom tags

One of the strong points for Liquex is that the tag parser can be extended to support non-standard tags. For example, Liquid used internally for the Shopify site includes a large range of tags that are not supported by the base Ruby gem. These tags could also be added to Liquex by extending the liquid parser.

defmodule CustomTag do
  import NimbleParsec
  alias Liquex.Parser.Base

  # Parse <<Custom Tag>>
  def custom_tag(combinator \\\\ empty()) do
    text =
      lookahead_not(string(">>"))
      |> utf8_char([])
      |> times(min: 1)
      |> reduce({Kernel, :to_string, []})
      |> tag(:text)

    combinator
    |> ignore(string("<<"))
    |> optional(text)
    |> ignore(string(">>"))
    |> tag(:custom_tag)
  end

  def element(combinator \\\\ empty()) do
    # Add the `custom_tag/1` parsing function to the supported element tag list
    combinator
    |> choice([custom_tag(), Base.base_element()])
  end
end

defmodule CustomParser do
  @moduledoc false
  import NimbleParsec

  defcombinatorp(:document, repeat(CustomTag.element()))
  defparsec(:parse, parsec(:document) |> eos())
end

iex> Liquex.parse("<<Hello World!>>", CustomParser)
iex> {:ok, [custom_tag: [text: ["Hello World!"]]]}

Custom renderer

In many cases, if you are building custom tags for your Liquid documents, you probably want to use a custom renderer. Just like the custom filters, you add your module to the context object.

defmodule CustomTagRender do
  def render({:custom_tag, contents}, context) do
    {result, context} = Liquex.render(contents, context)

    {["Custom Tag: ", result], context}
  end

  # Ignore this tag if we don't match
  def render(_, _), do: false
end

context = %Liquex.Context.new(%{}, render_module: CustomTagRender)

{:ok, document} = Liquex.parse("<<Hello World!>>", CustomParser)
{result, _} = Liquex.render(document, context)

result |> to_string()
iex> "Custom Tag: Hello World!"

roughike / liquex