Add helper function and change matcher so it converts keys to atoms o…

…nly if they already exist

lib/liquid.ex

@@ -42,4 +42,14 @@ defmodule Liquid do
     end
     def even_elements([]), do: []
   end
+
+  defmodule Atomizer do
+    def to_existing_atom(string) do
+      try do
+        String.to_existing_atom(string)
+      rescue
+        ArgumentError -> nil
+      end
+    end
+  end
 end

lib/protocols/matcher.ex

@@ -15,8 +15,8 @@ defimpl Liquid.Matcher, for: Liquid.Context do
     current = cond do
       current.assigns |> Map.has_key?(key) -> current.assigns
       current.presets |> Map.has_key?(key) -> current.presets
-      !(is_nil(Map.get(current.assigns, key |> String.to_atom))) -> current.assigns
-      !(is_nil(Map.get(current.presets, key |> String.to_atom))) -> current.presets
+      !(is_nil(Map.get(current.assigns, key |> Liquid.Atomizer.to_existing_atom))) -> current.assigns
+      !(is_nil(Map.get(current.presets, key |> Liquid.Atomizer.to_existing_atom))) -> current.presets
       is_map(current.assigns) and Map.has_key?(current.assigns, :__struct__) -> current.assigns
       true -> nil
     end
@@ -73,7 +73,7 @@ defimpl Liquid.Matcher, for: Any do
   end
 
   def match(current, key) when is_map(current) and is_binary(key) do
-    key = if Map.has_key?(current, :__struct__), do: key |> String.to_atom, else: key
+    key = if Map.has_key?(current, :__struct__), do: key |> Liquid.Atomizer.to_existing_atom, else: key
     current |> Map.get(key)
   end
 

mix.exs

@@ -3,7 +3,7 @@ defmodule Liquid.Mixfile do
 
   def project do
     [ app: :liquid,
-      version: "0.4.0",
+      version: "0.5.0",
       elixir: "~> 1.3",
       deps: deps,
       name: "Liquid",