From 588c5e21c74da1f0a576ad07f2d0f5336b8cd522 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Thu, 25 Jul 2024 10:42:43 -0400
Subject: [PATCH] Cache ItemSet#leading_item_sets return values - #28

---
 lib/propane/parser/item_set.rb | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/lib/propane/parser/item_set.rb b/lib/propane/parser/item_set.rb
index 41ca110..188436c 100644
--- a/lib/propane/parser/item_set.rb
+++ b/lib/propane/parser/item_set.rb
@@ -99,21 +99,24 @@ class Propane
       # @return [Set<ItemSet>]
       #   Set of all ItemSets that lead up to this ItemSet.
       def leading_item_sets
-        result = Set.new
-        eval_sets = Set[self]
-        evaled = Set.new
-        while eval_sets.size > 0
-          eval_set = eval_sets.first
-          eval_sets.delete(eval_set)
-          evaled << eval_set
-          eval_set.in_sets.each do |in_set|
-            result << in_set
-            unless evaled.include?(in_set)
-              eval_sets << in_set
+        @_leading_item_sets ||=
+          begin
+            result = Set.new
+            eval_sets = Set[self]
+            evaled = Set.new
+            while eval_sets.size > 0
+              eval_set = eval_sets.first
+              eval_sets.delete(eval_set)
+              evaled << eval_set
+              eval_set.in_sets.each do |in_set|
+                result << in_set
+                unless evaled.include?(in_set)
+                  eval_sets << in_set
+                end
+              end
             end
+            result
           end
-        end
-        result
       end
 
       # Represent the ItemSet as a String.