Determine the reduce actions for each parser state

lib/propane/parser/item.rb

@@ -86,10 +86,26 @@ class Propane
       # That is, the symbol which follows the parse position marker in the
       # current Item.
       #
+      # @param offset [Integer]
+      #   Offset from current parse position to examine.
+      #
       # @return [Token, RuleSet, nil]
       #   Following symbol for the Item.
-      def following_symbol
-        @rule.components[@position]
+      def following_symbol(offset = 0)
+        @rule.components[@position + offset]
+      end
+
+      # Get the previous symbol for the Item.
+      #
+      # That is, the symbol which precedes the parse position marker in the
+      # current Item.
+      #
+      # @return [Token, RuleSet, nil]
+      #   Previous symbol for this Item.
+      def previous_symbol
+        if @position > 0
+          @rule.components[@position - 1]
+        end
       end
 
       # Get whether this Item is followed by the provided symbol.

lib/propane/parser/item_set.rb

@@ -21,6 +21,14 @@ class Propane
       #   ItemSets leading to this item set.
       attr_reader :in_sets
 
+      # @return [Hash]
+      #   ItemSets reached from this item set. Key is a Token or Rule.
+      attr_reader :out_sets
+
+      # @return [nil, Rule, Hash]
+      #   Reduce actions, mapping lookahead tokens to rules.
+      attr_accessor :reduce_actions
+
       # Build an ItemSet.
       #
       # @param items [Array<Item>]
@@ -29,6 +37,7 @@ class Propane
         @items = Set.new(items)
         @following_item_set = {}
         @in_sets = Set.new
+        @out_sets = {}
         close!
       end