1 files changed, 81 insertions, 0 deletions
diff --git a/tool/lrama/lib/lrama/states/item.rb b/tool/lrama/lib/lrama/states/item.rb
new file mode 100644
index 0000000000..31b74b9d34
--- /dev/null
+++ b/tool/lrama/lib/lrama/states/item.rb
@@ -0,0 +1,81 @@
+# TODO: Validate position is not over rule rhs
+
+require "forwardable"
+
+module Lrama
+  class States
+    class Item < Struct.new(:rule, :position, keyword_init: true)
+      extend Forwardable
+
+      def_delegators "rule", :lhs, :rhs
+
+      # Optimization for States#setup_state
+      def hash
+        [rule_id, position].hash
+      end
+
+      def rule_id
+        rule.id
+      end
+
+      def empty_rule?
+        rule.empty_rule?
+      end
+
+      def number_of_rest_symbols
+        rhs.count - position
+      end
+
+      def next_sym
+        rhs[position]
+      end
+
+      def next_next_sym
+        rhs[position + 1]
+      end
+
+      def previous_sym
+        rhs[position - 1]
+      end
+
+      def end_of_rule?
+        rhs.count == position
+      end
+
+      def beginning_of_rule?
+        position == 0
+      end
+
+      def start_item?
+        rule.initial_rule? && beginning_of_rule?
+      end
+
+      def new_by_next_position
+        Item.new(rule: rule, position: position + 1)
+      end
+
+      def symbols_before_dot
+        rhs[0...position]
+      end
+
+      def symbols_after_dot
+        rhs[position..-1]
+      end
+
+      def to_s
+        "#{lhs.id.s_value}: #{display_name}"
+      end
+
+      def display_name
+        r = rhs.map(&:display_name).insert(position, "•").join(" ")
+        "#{r}  (rule #{rule_id})"
+      end
+
+      # Right after position
+      def display_rest
+        r = rhs[position..-1].map(&:display_name).join(" ")
+        ". #{r}  (rule #{rule_id})"
+      end
+    end
+  end
+end