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@@ -7,7 +7,7 @@ module Treetop
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         use_vars :result, :start_index
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         builder.assign "failed_alternatives", "[]"
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         compile_alternatives(alternatives)
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-        builder << "#{result_var}.dependencies.concat(failed_alternatives)"
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+        builder << "#{result_var}.add_dependencies(failed_alternatives)"
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         end_comment(self)
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       end
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@@ -63,7 +63,7 @@ module Treetop
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       end
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       def accumulate_dependency(dependency)
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-        builder.accumulate "#{result_var}.dependencies", dependency
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+        builder << "#{result_var}.add_dependencies([#{dependency}])"
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       end
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       def assign_result(value_ruby)

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@@ -16,7 +16,7 @@ module Treetop
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         builder.else_ do
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           assign_failure start_index_var
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           reset_index
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-          builder << "#{result_var}.dependencies.concat(#{accumulator_var})"
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+          builder << "#{result_var}.add_dependencies(#{accumulator_var})"
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         end
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         end_comment(self)
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       end

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@@ -1,7 +1,7 @@
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 module Treetop
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   module Runtime
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     class ParseResult
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-      attr_reader :dependent_results, :dependencies, :child_results, :dependents, :memoizations
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+      attr_reader :dependent_results, :dependencies, :child_results, :dependents, :memoizations, :refcount
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       attr_accessor :interval, :parent, :registered, :result_cache
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       alias :registered? :registered
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@@ -10,6 +10,31 @@ module Treetop
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         @dependencies = []
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         @dependents = []
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         @memoizations = []
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+        @refcount = 0
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+      end
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+
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+      def add_dependencies(new_dependencies)
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+        new_dependencies.each do |dependency|
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+          dependency.dependents.push(self)
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+        end
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+        dependencies.concat(new_dependencies)
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+      end
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+
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+      def retain(result_cache)
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+        if refcount == 0
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+          result_cache.results.push(self)
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+          @result_cache = result_cache
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+        end
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+
0
+        if child_results
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+          child_results.each do |child_result|
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+            child_result.retain(result_cache)
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+          end
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+        end
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+        dependencies.each do |dependency|
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+          dependency.retain(result_cache)
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+        end
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+        @refcount += 1
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       end
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       def expire(expire_parent=false)

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@@ -10,7 +10,7 @@ module Treetop
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       def store_result(rule_name, result)
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         result.memoizations.push(Memoization.new(rule_name, result, result_index))
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-        register_result(result)
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+        result.retain(self)
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       end
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       def get_result(rule_name, start_index)
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@@ -60,27 +60,6 @@ module Treetop
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       end
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       protected
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-      
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-      def register_result(result)
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-        return if result.registered?
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-        result.result_cache = self
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-
0
-        if result.child_results
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-          result.child_results.each do |child_result|
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-            child_result.parent = result
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-            register_result(child_result)
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-          end
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-        end
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-
0
-        result.dependencies.each do |subresult|
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-          subresult.dependents.push(result)
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-          register_result(subresult)
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-        end
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-
0
-        result.registered = true
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-        results.push(result)
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-      end
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-      
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       attr_reader :result_index, :results_to_delete, :memoizations_to_expire
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     end
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   end

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@@ -144,11 +144,11 @@ module ResultCacheSpec
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         @child = SyntaxNode.new(input, 0...5)
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         @epsilon_node = SyntaxNode.new(input, 5...5)
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         @predication_result = SyntaxNode.new(input, 5..8)
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-        epsilon_node.dependencies.push(predication_result)
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+        epsilon_node.add_dependencies([predication_result])
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         @parent = SyntaxNode.new(input, 0...5, [child, epsilon_node])
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         @non_local_dependency = TerminalParseFailure.new(5...15, 'x' * 10)
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0
-        parent.dependencies.push(non_local_dependency)
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+        parent.add_dependencies([non_local_dependency])
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         parent.dependencies.should == [non_local_dependency]
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         cache.store_result(:foo, parent)
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@@ -195,7 +195,7 @@ module ResultCacheSpec
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       before do
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         @grandchild = SyntaxNode.new(input,   3..5)
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         @dependency = SyntaxNode.new(input, 5...8)
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-        grandchild.dependencies.push(dependency)
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+        grandchild.add_dependencies([dependency])
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         @child = SyntaxNode.new(input, 0..5, [SyntaxNode.new(input, 0...3), grandchild])
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         @parent = SyntaxNode.new(input, 0..5, [child])
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