From 6026bf1514c68c985736d091787b3f3c811ea279 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Sun, 29 Aug 2021 09:41:00 -0400
Subject: [PATCH] Start building following item sets

---
 lib/imbecile/parser.rb          | 12 ++++++++++-
 lib/imbecile/parser/item.rb     | 26 ++++++++++++++++++++++++
 lib/imbecile/parser/item_set.rb | 35 +++++++++++++++++++++++++++++++++
 spec/imbecile_spec.rb           |  6 +++++-
 4 files changed, 77 insertions(+), 2 deletions(-)

diff --git a/lib/imbecile/parser.rb b/lib/imbecile/parser.rb
index 97789a2..2d3c90d 100644
--- a/lib/imbecile/parser.rb
+++ b/lib/imbecile/parser.rb
@@ -3,11 +3,21 @@ class Imbecile
   class Parser
 
     def initialize(tokens, rules)
+      @item_sets = []
+      item_sets_set = Set.new
       start_items = rules["Start"].patterns.map do |pattern|
         Item.new(pattern, 0)
       end
       start_item_set = ItemSet.new(start_items)
-      start_item_set.close!
+
+      puts "Start item set:"
+      puts start_item_set
+      start_item_set.follow_symbols.each do |follow_symbol|
+        follow_set = start_item_set.follow_set(follow_symbol)
+        puts
+        puts "follow set:"
+        puts follow_set
+      end
     end
 
   end
diff --git a/lib/imbecile/parser/item.rb b/lib/imbecile/parser/item.rb
index cf10336..8559c1d 100644
--- a/lib/imbecile/parser/item.rb
+++ b/lib/imbecile/parser/item.rb
@@ -37,6 +37,32 @@ class Imbecile
         end
       end
 
+      def follow_symbol
+        @pattern.components[@position]
+      end
+
+      def followed_by?(symbol)
+        follow_symbol == symbol
+      end
+
+      def next_position
+        Item.new(@pattern, @position + 1)
+      end
+
+      def to_s
+        parts = []
+        @pattern.components.each_with_index do |symbol, index|
+          if @position == index
+            parts << "."
+          end
+          parts << symbol.name
+        end
+        if @position == @pattern.components.size
+          parts << "."
+        end
+        parts.join(" ")
+      end
+
     end
 
   end
diff --git a/lib/imbecile/parser/item_set.rb b/lib/imbecile/parser/item_set.rb
index b77d4dc..8bc337d 100644
--- a/lib/imbecile/parser/item_set.rb
+++ b/lib/imbecile/parser/item_set.rb
@@ -3,10 +3,39 @@ class Imbecile
 
     class ItemSet
 
+      attr_reader :items
+
       def initialize(items)
         @items = Set.new(items)
+        close!
       end
 
+      def follow_symbols
+        Set.new(@items.map(&:follow_symbol))
+      end
+
+      def follow_set(symbol)
+        ItemSet.new(items_followed_by(symbol).map(&:next_position))
+      end
+
+      def hash
+        @items.hash
+      end
+
+      def ==(other)
+        @items.eql?(other.items)
+      end
+
+      def eql?(other)
+        self == other
+      end
+
+      def to_s
+        @items.map(&:to_s).join("\n")
+      end
+
+      private
+
       def close!
         eval_items = @items
         while eval_items.size > 0
@@ -19,6 +48,12 @@ class Imbecile
         end
       end
 
+      def items_followed_by(symbol)
+        @items.select do |item|
+          item.followed_by?(symbol)
+        end
+      end
+
     end
 
   end
diff --git a/spec/imbecile_spec.rb b/spec/imbecile_spec.rb
index 7424286..0bfa784 100644
--- a/spec/imbecile_spec.rb
+++ b/spec/imbecile_spec.rb
@@ -31,7 +31,11 @@ token int \\d+
 token plus \\+
 token times \\*
 drop \\s+
-Start: [] <<
+Start: [Foo] <<
+>>
+Foo: [int] <<
+>>
+Foo: [plus] <<
 >>
 EOF
     build_parser