Separate expression parsing and rendering from Context#resolve.

lib/liquid/range_lookup.rb

@@ -0,0 +1,22 @@
+module Liquid
+  class RangeLookup
+    def self.parse(start_markup, end_markup)
+      start_obj = Expression.parse(start_markup)
+      end_obj = Expression.parse(end_markup)
+      if start_obj.respond_to?(:evaluate) || end_obj.respond_to?(:evaluate)
+        new(start_obj, end_obj)
+      else
+        start_obj.to_i..end_obj.to_i
+      end
+    end
+
+    def initialize(start_obj, end_obj)
+      @start_obj = start_obj
+      @end_obj = end_obj
+    end
+
+    def evaluate(context)
+      context.evaluate(@start_obj).to_i..context.evaluate(@end_obj).to_i
+    end
+  end
+end