From 8b152abaa7306efa4ce6ca55a0046b0d05ae2b37 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Tue, 14 Jun 2022 07:34:35 -0400
Subject: [PATCH] Add ItemSet#leading_item_sets

---
 lib/propane/parser/item_set.rb | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/lib/propane/parser/item_set.rb b/lib/propane/parser/item_set.rb
index 3aacee9..df85c41 100644
--- a/lib/propane/parser/item_set.rb
+++ b/lib/propane/parser/item_set.rb
@@ -17,8 +17,8 @@ class Propane
       #   Maps a following symbol to its ItemSet.
       attr_reader :following_item_set
 
-      # @return [Set]
-      #   Item sets leading to this item set.
+      # @return [Set<ItemSet>]
+      #   ItemSets leading to this item set.
       attr_reader :in_sets
 
       # Build an ItemSet.
@@ -81,6 +81,18 @@ class Propane
         self == other
       end
 
+      # Set of ItemSets that lead to this ItemSet.
+      #
+      # This set includes this ItemSet.
+      #
+      # @return [Set<ItemSet>]
+      #   Set of all ItemSets that lead up to this ItemSet.
+      def leading_item_sets
+        @in_sets.reduce(Set[self]) do |result, item_set|
+          result + item_set.leading_item_sets
+        end
+      end
+
       # Represent the ItemSet as a String.
       #
       # @return [String]