Separate expression parsing and rendering from Context#resolve.

lib/liquid/expression.rb

@@ -0,0 +1,33 @@
+module Liquid
+  class Expression
+    LITERALS = {
+      nil => nil, 'nil'.freeze => nil, 'null'.freeze => nil, ''.freeze => nil,
+      'true'.freeze  => true,
+      'false'.freeze => false,
+      'blank'.freeze => :blank?,
+      'empty'.freeze => :empty?
+    }
+
+    def self.parse(markup)
+      if LITERALS.key?(markup)
+        LITERALS[markup]
+      else
+        case markup
+        when /\A'(.*)'\z/m # Single quoted strings
+          $1
+        when /\A"(.*)"\z/m # Double quoted strings
+          $1
+        when /\A(-?\d+)\z/ # Integer and floats
+          $1.to_i
+        when /\A\((\S+)\.\.(\S+)\)\z/ # Ranges
+          RangeLookup.parse($1, $2)
+        when /\A(-?\d[\d\.]+)\z/ # Floats
+          $1.to_f
+        else
+          VariableLookup.parse(markup)
+        end
+      end
+    end
+
+  end
+end