1 files changed, 23 insertions, 6 deletions
diff --git a/tool/lrama/lib/lrama/grammar/parameterizing_rules/builder.rb b/tool/lrama/lib/lrama/grammar/parameterizing_rules/builder.rb
index 28c9ad427d..20950b9b36 100644
--- a/tool/lrama/lib/lrama/grammar/parameterizing_rules/builder.rb
+++ b/tool/lrama/lib/lrama/grammar/parameterizing_rules/builder.rb
@@ -8,6 +8,7 @@ require 'lrama/grammar/parameterizing_rules/builder/separated_list'
 module Lrama
   class Grammar
     class ParameterizingRules
+      # Builder for parameterizing rules
       class Builder
         RULES = {
           option: Lrama::Grammar::ParameterizingRules::Builder::Option,
@@ -20,23 +21,39 @@ module Lrama
           separated_list: Lrama::Grammar::ParameterizingRules::Builder::SeparatedList,
         }
 
-        def initialize(token, rule_counter, lhs, user_code, precedence_sym, line)
+        def initialize(token, rule_counter, lhs_tag, user_code, precedence_sym, line)
           @token = token
           @key = token.s_value.to_sym
           @rule_counter = rule_counter
-          @lhs = lhs
+          @lhs_tag = lhs_tag
           @user_code = user_code
           @precedence_sym = precedence_sym
           @line = line
+          @builder = nil
         end
 
         def build
-          if RULES.key?(@key)
-            RULES[@key].new(@token, @rule_counter, @lhs, @user_code, @precedence_sym, @line).build
-          else
-            raise "Parameterizing rule does not exist. `#{@key}`"
+          create_builder
+          @builder.build
+        end
+
+        def build_token
+          create_builder
+          @builder.build_token
+        end
+
+        private
+
+        def create_builder
+          unless @builder
+            validate_key!
+            @builder = RULES[@key].new(@token, @rule_counter, @lhs_tag, @user_code, @precedence_sym, @line)
           end
         end
+
+        def validate_key!
+          raise "Parameterizing rule does not exist. `#{@key}`" unless RULES.key?(@key)
+        end
       end
     end
   end