Use \G to force Regexps to match only at the first position

lib/treetop/compiler/node_classes/character_class.rb

@@ -4,7 +4,7 @@ class CharacterClass < AtomicExpression
       def compile(address, builder, parent_expression = nil)
         super
 
-        builder.if__ "input.index(Regexp.new(#{single_quote(text_value)}), index) == index" do
+        builder.if__ "input.index(Regexp.new(#{grounded_regexp(text_value)}), index) == index" do
           assign_result "instantiate_node(#{node_class_name},input, index...(index + 1))"
           extend_result_with_inline_module
           builder << "@index += 1"
@@ -14,6 +14,11 @@ def compile(address, builder, parent_expression = nil)
           assign_result 'nil'
         end
       end
+
+      def grounded_regexp(string)
+        # Double any backslashes, then backslash any single-quotes:
+        "'\\G#{string.gsub(/\\/) { '\\\\' }.gsub(/'/) { "\\'"}}'"
+      end
     end
   end
 end