From 5af3179ff2766e095ffb2c09790da6031ebb893c Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Wed, 15 Jun 2022 23:27:19 -0400
Subject: [PATCH] Add RuleSet#start_token_set

---
 lib/propane/rule_set.rb | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/lib/propane/rule_set.rb b/lib/propane/rule_set.rb
index a47054c..fb6c101 100644
--- a/lib/propane/rule_set.rb
+++ b/lib/propane/rule_set.rb
@@ -40,6 +40,30 @@ class Propane
       @could_be_empty
     end
 
+    # Build the start token set for the RuleSet.
+    #
+    # @return [Set<Token>]
+    #   Start token set for the RuleSet.
+    def start_token_set
+      if @_start_token_set.nil?
+        @_start_token_set = Set.new
+        @rules.each do |rule|
+          rule.components.each do |component|
+            if component.is_a?(Token)
+              @_start_token_set << component
+              break
+            else
+              @_start_token_set += component.start_token_set
+              unless component.could_be_empty?
+                break
+              end
+            end
+          end
+        end
+      end
+      @_start_token_set
+    end
+
   end
 
 end