Lrama v0.5.4

27 files changed, 871 insertions, 168 deletions

diff --git a/tool/lrama/lib/lrama.rb b/tool/lrama/lib/lrama.rb
index 19f579c330..12e635d8b6 100644
--- a/tool/lrama/lib/lrama.rb
+++ b/tool/lrama/lib/lrama.rb
@@ -1,6 +1,7 @@
 require "lrama/bitmap"
 require "lrama/command"
 require "lrama/context"
+require "lrama/counterexamples"
 require "lrama/digraph"
 require "lrama/grammar"
 require "lrama/lexer"
@@ -10,5 +11,6 @@ require "lrama/report"
 require "lrama/state"
 require "lrama/states"
 require "lrama/states_reporter"
+require "lrama/type"
 require "lrama/version"
 require "lrama/warning"
diff --git a/tool/lrama/lib/lrama/command.rb b/tool/lrama/lib/lrama/command.rb
index 2d37639d69..9fceb55fe0 100644
--- a/tool/lrama/lib/lrama/command.rb
+++ b/tool/lrama/lib/lrama/command.rb
@@ -67,7 +67,7 @@ module Lrama
       bison_list = %w[states itemsets lookaheads solved counterexamples cex all none]
       others = %w[verbose]
       list = bison_list + others
-      not_supported = %w[counterexamples cex none]
+      not_supported = %w[cex none]
       h = { grammar: true }
 
       report.each do |r|
@@ -121,13 +121,13 @@ module Lrama
       # Output Files:
       opt.on('-h', '--header=[FILE]') {|v| @header = true; @header_file = v }
       opt.on('-d') { @header = true }
-      opt.on('-r', '--report=THINGS') {|v| @report = v.split(',') }
+      opt.on('-r', '--report=THINGS', Array) {|v| @report = v }
       opt.on('--report-file=FILE')    {|v| @report_file = v }
       opt.on('-v') {  } # Do nothing
       opt.on('-o', '--output=FILE')   {|v| @outfile = v }
 
       # Hidden
-      opt.on('--trace=THINGS') {|v| @trace = v.split(',') }
+      opt.on('--trace=THINGS', Array) {|v| @trace = v }
 
       # Error Recovery
       opt.on('-e') {|v| @error_recovery = true }
diff --git a/tool/lrama/lib/lrama/counterexamples.rb b/tool/lrama/lib/lrama/counterexamples.rb
new file mode 100644
index 0000000000..a5d62a0c7c
--- /dev/null
+++ b/tool/lrama/lib/lrama/counterexamples.rb
@@ -0,0 +1,285 @@
+require "set"
+
+require "lrama/counterexamples/derivation"
+require "lrama/counterexamples/example"
+require "lrama/counterexamples/path"
+require "lrama/counterexamples/state_item"
+require "lrama/counterexamples/triple"
+
+module Lrama
+  # See: https://www.cs.cornell.edu/andru/papers/cupex/cupex.pdf
+  #      4. Constructing Nonunifying Counterexamples
+  class Counterexamples
+    attr_reader :transitions, :productions
+
+    def initialize(states)
+      @states = states
+      setup_transitions
+      setup_productions
+    end
+
+    def to_s
+      "#<Counterexamples>"
+    end
+    alias :inspect :to_s
+
+    def compute(conflict_state)
+      conflict_state.conflicts.flat_map do |conflict|
+        case conflict.type
+        when :shift_reduce
+          shift_reduce_example(conflict_state, conflict)
+        when :reduce_reduce
+          reduce_reduce_examples(conflict_state, conflict)
+        end
+      end.compact
+    end
+
+    private
+
+    def setup_transitions
+      # Hash [StateItem, Symbol] => StateItem
+      @transitions = {}
+      # Hash [StateItem, Symbol] => Set(StateItem)
+      @reverse_transitions = {}
+
+      @states.states.each do |src_state|
+        trans = {}
+
+        src_state.transitions.each do |shift, next_state|
+          trans[shift.next_sym] = next_state
+        end
+
+        src_state.items.each do |src_item|
+          next if src_item.end_of_rule?
+          sym = src_item.next_sym
+          dest_state = trans[sym]
+
+          dest_state.kernels.each do |dest_item|
+            next unless (src_item.rule == dest_item.rule) && (src_item.position + 1 == dest_item.position)
+            src_state_item = StateItem.new(src_state, src_item)
+            dest_state_item = StateItem.new(dest_state, dest_item)
+
+            @transitions[[src_state_item, sym]] = dest_state_item
+
+            key = [dest_state_item, sym]
+            @reverse_transitions[key] ||= Set.new
+            @reverse_transitions[key] << src_state_item
+          end
+        end
+      end
+    end
+
+    def setup_productions
+      # Hash [StateItem] => Set(Item)
+      @productions = {}
+      # Hash [State, Symbol] => Set(Item). Symbol is nterm
+      @reverse_productions = {}
+
+      @states.states.each do |state|
+        # LHS => Set(Item)
+        h = {}
+
+        state.closure.each do |item|
+          sym = item.lhs
+
+          h[sym] ||= Set.new
+          h[sym] << item
+        end
+
+        state.items.each do |item|
+          next if item.end_of_rule?
+          next if item.next_sym.term?
+
+          sym = item.next_sym
+          state_item = StateItem.new(state, item)
+          key = [state, sym]
+
+          @productions[state_item] = h[sym]
+
+          @reverse_productions[key] ||= Set.new
+          @reverse_productions[key] << item
+        end
+      end
+    end
+
+    def shift_reduce_example(conflict_state, conflict)
+      conflict_symbol = conflict.symbols.first
+      shift_conflict_item = conflict_state.items.find { |item| item.next_sym == conflict_symbol }
+      path2 = shortest_path(conflict_state, conflict.reduce.item, conflict_symbol)
+      path1 = find_shift_conflict_shortest_path(path2, conflict_state, shift_conflict_item)
+
+      Example.new(path1, path2, conflict, conflict_symbol, self)
+    end
+
+    def reduce_reduce_examples(conflict_state, conflict)
+      conflict_symbol = conflict.symbols.first
+      path1 = shortest_path(conflict_state, conflict.reduce1.item, conflict_symbol)
+      path2 = shortest_path(conflict_state, conflict.reduce2.item, conflict_symbol)
+
+      Example.new(path1, path2, conflict, conflict_symbol, self)
+    end
+
+    def find_shift_conflict_shortest_path(reduce_path, conflict_state, conflict_item)
+      state_items = find_shift_conflict_shortest_state_items(reduce_path, conflict_state, conflict_item)
+      build_paths_from_state_items(state_items)
+    end
+
+    def find_shift_conflict_shortest_state_items(reduce_path, conflict_state, conflict_item)
+      target_state_item = StateItem.new(conflict_state, conflict_item)
+      result = [target_state_item]
+      reversed_reduce_path = reduce_path.to_a.reverse
+      # Index for state_item
+      i = 0
+
+      while (path = reversed_reduce_path[i])
+        # Index for prev_state_item
+        j = i + 1
+        _j = j
+
+        while (prev_path = reversed_reduce_path[j])
+          if prev_path.production?
+            j += 1
+          else
+            break
+          end
+        end
+
+        state_item = path.to
+        prev_state_item = prev_path&.to
+
+        if target_state_item == state_item || target_state_item.item.start_item?
+          result.concat(reversed_reduce_path[_j..-1].map(&:to))
+          break
+        end
+
+        if target_state_item.item.beginning_of_rule?
+          queue = []
+          queue << [target_state_item]
+
+          # Find reverse production
+          while (sis = queue.shift)
+            si = sis.last
+
+            # Reach to start state
+            if si.item.start_item?
+              sis.shift
+              result.concat(sis)
+              target_state_item = si
+              break
+            end
+
+            if !si.item.beginning_of_rule?
+              key = [si, si.item.previous_sym]
+              @reverse_transitions[key].each do |prev_target_state_item|
+                next if prev_target_state_item.state != prev_state_item.state
+                sis.shift
+                result.concat(sis)
+                result << prev_target_state_item
+                target_state_item = prev_target_state_item
+                i = j
+                queue.clear
+                break
+              end
+            else
+              key = [si.state, si.item.lhs]
+              @reverse_productions[key].each do |item|
+                state_item = StateItem.new(si.state, item)
+                queue << (sis + [state_item])
+              end
+            end
+          end
+        else
+          # Find reverse transition
+          key = [target_state_item, target_state_item.item.previous_sym]
+          @reverse_transitions[key].each do |prev_target_state_item|
+            next if prev_target_state_item.state != prev_state_item.state
+            result << prev_target_state_item
+            target_state_item = prev_target_state_item
+            i = j
+            break
+          end
+        end
+      end
+
+      result.reverse
+    end
+
+    def build_paths_from_state_items(state_items)
+      paths = state_items.zip([nil] + state_items).map do |si, prev_si|
+        case
+        when prev_si.nil?
+          StartPath.new(si)
+        when si.item.beginning_of_rule?
+          ProductionPath.new(prev_si, si)
+        else
+          TransitionPath.new(prev_si, si)
+        end
+      end
+
+      paths
+    end
+
+    def shortest_path(conflict_state, conflict_reduce_item, conflict_term)
+      # queue: is an array of [Triple, [Path]]
+      queue = []
+      visited = {}
+      start_state = @states.states.first
+      raise "BUG: Start state should be just one kernel." if start_state.kernels.count != 1
+
+      start = Triple.new(start_state, start_state.kernels.first, Set.new([@states.eof_symbol]))
+
+      queue << [start, [StartPath.new(start.state_item)]]
+
+      while true
+        triple, paths = queue.shift
+
+        next if visited[triple]
+        visited[triple] = true
+
+        # Found
+        if triple.state == conflict_state && triple.item == conflict_reduce_item && triple.l.include?(conflict_term)
+          return paths
+        end
+
+        # transition
+        triple.state.transitions.each do |shift, next_state|
+          next unless triple.item.next_sym && triple.item.next_sym == shift.next_sym
+          next_state.kernels.each do |kernel|
+            next if kernel.rule != triple.item.rule
+            t = Triple.new(next_state, kernel, triple.l)
+            queue << [t, paths + [TransitionPath.new(triple.state_item, t.state_item)]]
+          end
+        end
+
+        # production step
+        triple.state.closure.each do |item|
+          next unless triple.item.next_sym && triple.item.next_sym == item.lhs
+          l = follow_l(triple.item, triple.l)
+          t = Triple.new(triple.state, item, l)
+          queue << [t, paths + [ProductionPath.new(triple.state_item, t.state_item)]]
+        end
+
+        break if queue.empty?
+      end
+
+      return nil
+    end
+
+    def follow_l(item, current_l)
+      # 1. follow_L (A -> X1 ... Xn-1 • Xn) = L
+      # 2. follow_L (A -> X1 ... Xk • Xk+1 Xk+2 ... Xn) = {Xk+2} if Xk+2 is a terminal
+      # 3. follow_L (A -> X1 ... Xk • Xk+1 Xk+2 ... Xn) = FIRST(Xk+2) if Xk+2 is a nonnullable nonterminal
+      # 4. follow_L (A -> X1 ... Xk • Xk+1 Xk+2 ... Xn) = FIRST(Xk+2) + follow_L (A -> X1 ... Xk+1 • Xk+2 ... Xn) if Xk+2 is a nullable nonterminal
+      case
+      when item.number_of_rest_symbols == 1
+        current_l
+      when item.next_next_sym.term?
+        Set.new([item.next_next_sym])
+      when !item.next_next_sym.nullable
+        item.next_next_sym.first_set
+      else
+        item.next_next_sym.first_set + follow_l(item.new_by_next_position, current_l)
+      end
+    end
+  end
+end
diff --git a/tool/lrama/lib/lrama/counterexamples/derivation.rb b/tool/lrama/lib/lrama/counterexamples/derivation.rb
new file mode 100644
index 0000000000..691e935356
--- /dev/null
+++ b/tool/lrama/lib/lrama/counterexamples/derivation.rb
@@ -0,0 +1,63 @@
+module Lrama
+  class Counterexamples
+    class Derivation
+      attr_reader :item, :left, :right
+      attr_writer :right
+
+      def initialize(item, left, right = nil)
+        @item = item
+        @left = left
+        @right = right
+      end
+
+      def to_s
+        "#<Derivation(#{item.display_name})>"
+      end
+      alias :inspect :to_s
+
+      def render_strings_for_report
+        result = []
+        _render_for_report(self, 0, result, 0)
+        result.map(&:rstrip)
+      end
+
+      def render_for_report
+        render_strings_for_report.join("\n")
+      end
+
+      private
+
+      def _render_for_report(derivation, offset, strings, index)
+        item = derivation.item
+        if strings[index]
+          strings[index] << " " * (offset - strings[index].length)
+        else
+          strings[index] = " " * offset
+        end
+        str = strings[index]
+        str << "#{item.rule_id}: #{item.symbols_before_dot.map(&:display_name).join(" ")} "
+
+        if derivation.left
+          len = str.length
+          str << "#{item.next_sym.display_name}"
+          length = _render_for_report(derivation.left, len, strings, index + 1)
+          # I want String#ljust!
+          str << " " * (length - str.length)
+        else
+          str << " • #{item.symbols_after_dot.map(&:display_name).join(" ")} "
+          return str.length
+        end
+
+        if derivation.right&.left
+          length = _render_for_report(derivation.right.left, str.length, strings, index + 1)
+          str << "#{item.symbols_after_dot[1..-1].map(&:display_name).join(" ")} "
+          str << " " * (length - str.length) if length > str.length
+        elsif item.next_next_sym
+          str << "#{item.symbols_after_dot[1..-1].map(&:display_name).join(" ")} "
+        end
+
+        return str.length
+      end
+    end
+  end
+end
diff --git a/tool/lrama/lib/lrama/counterexamples/example.rb b/tool/lrama/lib/lrama/counterexamples/example.rb
new file mode 100644
index 0000000000..8f02d71fa4
--- /dev/null
+++ b/tool/lrama/lib/lrama/counterexamples/example.rb
@@ -0,0 +1,124 @@
+module Lrama
+  class Counterexamples
+    class Example
+      attr_reader :path1, :path2, :conflict, :conflict_symbol
+
+      # path1 is shift conflict when S/R conflict
+      # path2 is always reduce conflict
+      def initialize(path1, path2, conflict, conflict_symbol, counterexamples)
+        @path1 = path1
+        @path2 = path2
+        @conflict = conflict
+        @conflict_symbol = conflict_symbol
+        @counterexamples = counterexamples
+      end
+
+      def type
+        @conflict.type
+      end
+
+      def path1_item
+        @path1.last.to.item
+      end
+
+      def path2_item
+        @path2.last.to.item
+      end
+
+      def derivations1
+        @derivations1 ||= _derivations(path1)
+      end
+
+      def derivations2
+        @derivations2 ||= _derivations(path2)
+      end
+
+      private
+
+      def _derivations(paths)
+        derivation = nil
+        current = :production
+        lookahead_sym = paths.last.to.item.end_of_rule? ? @conflict_symbol : nil
+
+        paths.reverse.each do |path|
+          item = path.to.item
+
+          case current
+          when :production
+            case path
+            when StartPath
+              derivation = Derivation.new(item, derivation)
+              current = :start
+            when TransitionPath
+              derivation = Derivation.new(item, derivation)
+              current = :transition
+            when ProductionPath
+              derivation = Derivation.new(item, derivation)
+              current = :production
+            end
+
+            if lookahead_sym && item.next_next_sym && item.next_next_sym.first_set.include?(lookahead_sym)
+              state_item = @counterexamples.transitions[[path.to, item.next_sym]]
+              derivation2 = find_derivation_for_symbol(state_item, lookahead_sym)
+              derivation.right = derivation2
+              lookahead_sym = nil
+            end
+
+          when :transition
+            case path
+            when StartPath
+              derivation = Derivation.new(item, derivation)
+              current = :start
+            when TransitionPath
+              # ignore
+              current = :transition
+            when ProductionPath
+              # ignore
+              current = :production
+            end
+          else
+            raise "BUG: Unknown #{current}"
+          end
+
+          break if current == :start
+        end
+
+        derivation
+      end
+
+      def find_derivation_for_symbol(state_item, sym)
+        queue = []
+        queue << [state_item]
+
+        while (sis = queue.shift)
+          si = sis.last
+          next_sym = si.item.next_sym
+
+          if next_sym == sym
+            derivation = nil
+
+            sis.reverse.each do |si|
+              derivation = Derivation.new(si.item, derivation)
+            end
+
+            return derivation
+          end
+
+          if next_sym.nterm? && next_sym.first_set.include?(sym)
+            @counterexamples.productions[si].each do |next_item|
+              next if next_item.empty_rule?
+              next_si = StateItem.new(si.state, next_item)
+              next if sis.include?(next_si)
+              queue << (sis + [next_si])
+            end
+
+            if next_sym.nullable
+              next_si = @counterexamples.transitions[[si, next_sym]]
+              queue << (sis + [next_si])
+            end
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/tool/lrama/lib/lrama/counterexamples/path.rb b/tool/lrama/lib/lrama/counterexamples/path.rb
new file mode 100644
index 0000000000..a4caecd765
--- /dev/null
+++ b/tool/lrama/lib/lrama/counterexamples/path.rb
@@ -0,0 +1,69 @@
+module Lrama
+  class Counterexamples
+    class Path
+      def initialize(from_state_item, to_state_item)
+        @from_state_item = from_state_item
+        @to_state_item = to_state_item
+      end
+
+      def from
+        @from_state_item
+      end
+
+      def to
+        @to_state_item
+      end
+
+      def to_s
+        "#<Path(#{type})>"
+      end
+      alias :inspect :to_s
+    end
+
+    class StartPath < Path
+      def initialize(to_state_item)
+        super nil, to_state_item
+      end
+
+      def type
+        :start
+      end
+
+      def transition?
+        false
+      end
+
+      def production?
+        false
+      end
+    end
+
+    class TransitionPath < Path
+      def type
+        :transition
+      end
+
+      def transition?
+        true
+      end
+
+      def production?
+        false
+      end
+    end
+
+    class ProductionPath < Path
+      def type
+        :production
+      end
+
+      def transition?
+        false
+      end
+
+      def production?
+        true
+      end
+    end
+  end
+end
diff --git a/tool/lrama/lib/lrama/counterexamples/state_item.rb b/tool/lrama/lib/lrama/counterexamples/state_item.rb
new file mode 100644
index 0000000000..930ff4a5f8
--- /dev/null
+++ b/tool/lrama/lib/lrama/counterexamples/state_item.rb
@@ -0,0 +1,6 @@
+module Lrama
+  class Counterexamples
+    class StateItem < Struct.new(:state, :item)
+    end
+  end
+end
diff --git a/tool/lrama/lib/lrama/counterexamples/triple.rb b/tool/lrama/lib/lrama/counterexamples/triple.rb
new file mode 100644
index 0000000000..e802beccf4
--- /dev/null
+++ b/tool/lrama/lib/lrama/counterexamples/triple.rb
@@ -0,0 +1,21 @@
+module Lrama
+  class Counterexamples
+    # s: state
+    # itm: item within s
+    # l: precise lookahead set
+    class Triple < Struct.new(:s, :itm, :l)
+      alias :state :s
+      alias :item :itm
+      alias :precise_lookahead_set :l
+
+      def state_item
+        StateItem.new(state, item)
+      end
+
+      def inspect
+        "#{state.inspect}. #{item.display_name}. #{l.map(&:id).map(&:s_value)}"
+      end
+      alias :to_s :inspect
+    end
+  end
+end
diff --git a/tool/lrama/lib/lrama/digraph.rb b/tool/lrama/lib/lrama/digraph.rb
index 28f26781b1..c48b3f4041 100644
--- a/tool/lrama/lib/lrama/digraph.rb
+++ b/tool/lrama/lib/lrama/digraph.rb
@@ -33,7 +33,7 @@ module Lrama
       @h[x] = d
       @result[x] = @base_function[x] # F x = F' x
 
-      @relation[x] && @relation[x].each do |y|
+      @relation[x]&.each do |y|
         traverse(y) if @h[y] == 0
         @h[x] = [@h[x], @h[y]].min
         @result[x] |= @result[y] # F x = F x + F y
@@ -43,9 +43,8 @@ module Lrama
         while true do
           z = @stack.pop
           @h[z] = Float::INFINITY
-          @result[z] = @result[x] # F (Top of S) = F x
-
           break if z == x
+          @result[z] = @result[x] # F (Top of S) = F x
         end
       end
     end
diff --git a/tool/lrama/lib/lrama/grammar.rb b/tool/lrama/lib/lrama/grammar.rb
index a4f98ecc83..25f1a49170 100644
--- a/tool/lrama/lib/lrama/grammar.rb
+++ b/tool/lrama/lib/lrama/grammar.rb
@@ -1,3 +1,4 @@
+require "lrama/grammar/auxiliary"
 require "lrama/grammar/code"
 require "lrama/grammar/error_token"
 require "lrama/grammar/precedence"
@@ -7,16 +8,13 @@ require "lrama/grammar/rule"
 require "lrama/grammar/symbol"
 require "lrama/grammar/union"
 require "lrama/lexer"
+require "lrama/type"
 
 module Lrama
-  Type = Struct.new(:id, :tag, keyword_init: true)
   Token = Lrama::Lexer::Token
 
   # Grammar is the result of parsing an input grammar file
   class Grammar
-    # Grammar file information not used by States but by Output
-    Aux = Struct.new(:prologue_first_lineno, :prologue, :epilogue_first_lineno, :epilogue, keyword_init: true)
-
     attr_reader :eof_symbol, :error_symbol, :undef_symbol, :accept_symbol, :aux
     attr_accessor :union, :expect,
                   :printers, :error_tokens,
@@ -38,7 +36,7 @@ module Lrama
       @error_symbol = nil
       @undef_symbol = nil
       @accept_symbol = nil
-      @aux = Aux.new
+      @aux = Auxiliary.new
 
       append_special_symbols
     end
@@ -48,7 +46,7 @@ module Lrama
     end
 
     def add_error_token(ident_or_tags:, code:, lineno:)
-      @error_tokens << ErrorToken.new(ident_or_tags, code, lineno)
+      @error_tokens << ErrorToken.new(ident_or_tags: ident_or_tags, code: code, lineno: lineno)
     end
 
     def add_term(id:, alias_name: nil, tag: nil, token_id: nil, replace: false)
@@ -215,6 +213,41 @@ module Lrama
       end
     end
 
+    def compute_first_set
+      terms.each do |term|
+        term.first_set = Set.new([term]).freeze
+        term.first_set_bitmap = Lrama::Bitmap.from_array([term.number])
+      end
+
+      nterms.each do |nterm|
+        nterm.first_set = Set.new([]).freeze
+        nterm.first_set_bitmap = Lrama::Bitmap.from_array([])
+      end
+
+      while true do
+        changed = false
+
+        @rules.each do |rule|
+          rule.rhs.each do |r|
+            if rule.lhs.first_set_bitmap | r.first_set_bitmap != rule.lhs.first_set_bitmap
+              changed = true
+              rule.lhs.first_set_bitmap = rule.lhs.first_set_bitmap | r.first_set_bitmap
+            end
+
+            break unless r.nullable
+          end
+        end
+
+        break unless changed
+      end
+
+      nterms.each do |nterm|
+        nterm.first_set = Lrama::Bitmap.to_array(nterm.first_set_bitmap).map do |number|
+          find_symbol_by_number!(number)
+        end.to_set
+      end
+    end
+
     def find_symbol_by_s_value(s_value)
       @symbols.find do |sym|
         sym.id.s_value == s_value
diff --git a/tool/lrama/lib/lrama/grammar/auxiliary.rb b/tool/lrama/lib/lrama/grammar/auxiliary.rb
new file mode 100644
index 0000000000..933574b0f6
--- /dev/null
+++ b/tool/lrama/lib/lrama/grammar/auxiliary.rb
@@ -0,0 +1,7 @@
+module Lrama
+  class Grammar
+    # Grammar file information not used by States but by Output
+    class Auxiliary < Struct.new(:prologue_first_lineno, :prologue, :epilogue_first_lineno, :epilogue, keyword_init: true)
+    end
+  end
+end
diff --git a/tool/lrama/lib/lrama/grammar/rule.rb b/tool/lrama/lib/lrama/grammar/rule.rb
index 7ed5b3312c..c559388b62 100644
--- a/tool/lrama/lib/lrama/grammar/rule.rb
+++ b/tool/lrama/lib/lrama/grammar/rule.rb
@@ -17,6 +17,12 @@ module Lrama
         "#{l}: #{r}"
       end
 
+      # opt_nl: ε     <-- empty_rule
+      #       | '\n'  <-- not empty_rule
+      def empty_rule?
+        rhs.empty?
+      end
+
       def precedence
         precedence_sym&.precedence
       end
diff --git a/tool/lrama/lib/lrama/grammar/symbol.rb b/tool/lrama/lib/lrama/grammar/symbol.rb
index 28916eb54f..9df1c2f636 100644
--- a/tool/lrama/lib/lrama/grammar/symbol.rb
+++ b/tool/lrama/lib/lrama/grammar/symbol.rb
@@ -7,6 +7,7 @@
 module Lrama
   class Grammar
     class Symbol < Struct.new(:id, :alias_name, :number, :tag, :term, :token_id, :nullable, :precedence, :printer, :error_token, keyword_init: true)
+      attr_accessor :first_set, :first_set_bitmap
       attr_writer :eof_symbol, :error_symbol, :undef_symbol, :accept_symbol
 
       def term?
@@ -34,11 +35,7 @@ module Lrama
       end
 
       def display_name
-        if alias_name
-          alias_name
-        else
-          id.s_value
-        end
+        alias_name || id.s_value
       end
 
       # name for yysymbol_kind_t
@@ -51,11 +48,7 @@ module Lrama
         when eof_symbol?
           name = "YYEOF"
         when term? && id.type == Token::Char
-          if alias_name
-            name = number.to_s + alias_name
-          else
-            name = number.to_s + id.s_value
-          end
+          name = number.to_s + display_name
         when term? && id.type == Token::Ident
           name = id.s_value
         when nterm? && (id.s_value.include?("$") || id.s_value.include?("@"))
@@ -66,7 +59,7 @@ module Lrama
           raise "Unexpected #{self}"
         end
 
-        "YYSYMBOL_" + name.gsub(/[^a-zA-Z_0-9]+/, "_")
+        "YYSYMBOL_" + name.gsub(/\W+/, "_")
       end
 
       # comment for yysymbol_kind_t
diff --git a/tool/lrama/lib/lrama/lexer/token.rb b/tool/lrama/lib/lrama/lexer/token.rb
index 29ce48b2fa..aa49bfe47d 100644
--- a/tool/lrama/lib/lrama/lexer/token.rb
+++ b/tool/lrama/lib/lrama/lexer/token.rb
@@ -1,7 +1,8 @@
+require 'lrama/lexer/token/type'
+
 module Lrama
   class Lexer
-    class Token < Struct.new(:type, :s_value, :alias, keyword_init: true)
-      Type = Struct.new(:id, :name, keyword_init: true)
+    class Token
 
       attr_accessor :line, :column, :referred
       # For User_code
diff --git a/tool/lrama/lib/lrama/lexer/token/type.rb b/tool/lrama/lib/lrama/lexer/token/type.rb
new file mode 100644
index 0000000000..d58a56f40b
--- /dev/null
+++ b/tool/lrama/lib/lrama/lexer/token/type.rb
@@ -0,0 +1,8 @@
+module Lrama
+  class Lexer
+    class Token < Struct.new(:type, :s_value, :alias, keyword_init: true)
+      class Type < Struct.new(:id, :name, keyword_init: true)
+      end
+    end
+  end
+end
diff --git a/tool/lrama/lib/lrama/output.rb b/tool/lrama/lib/lrama/output.rb
index dd71814a11..757d16e25a 100644
--- a/tool/lrama/lib/lrama/output.rb
+++ b/tool/lrama/lib/lrama/output.rb
@@ -252,7 +252,7 @@ module Lrama
     end
 
     def extract_param_name(param)
-      /\A(.)+([a-zA-Z0-9_]+)\z/.match(param)[2]
+      /\A(\W*)([a-zA-Z0-9_]+)\z/.match(param.split.last)[2]
     end
 
     def parse_param_name
diff --git a/tool/lrama/lib/lrama/parser.rb b/tool/lrama/lib/lrama/parser.rb
index 4faa402d1b..a12c8bbb34 100644
--- a/tool/lrama/lib/lrama/parser.rb
+++ b/tool/lrama/lib/lrama/parser.rb
@@ -22,6 +22,7 @@ module Lrama
         process_epilogue(grammar, lexer)
         grammar.prepare
         grammar.compute_nullable
+        grammar.compute_first_set
         grammar.validate!
 
         grammar
diff --git a/tool/lrama/lib/lrama/parser/token_scanner.rb b/tool/lrama/lib/lrama/parser/token_scanner.rb
index 1ff67b30a3..992b5742d3 100644
--- a/tool/lrama/lib/lrama/parser/token_scanner.rb
+++ b/tool/lrama/lib/lrama/parser/token_scanner.rb
@@ -11,7 +11,7 @@ module Lrama
       end
 
       def current_type
-        current_token && current_token.type
+        current_token&.type
       end
 
       def previous_token
@@ -26,9 +26,7 @@ module Lrama
 
       def consume(*token_types)
         if token_types.include?(current_type)
-          token = current_token
-          self.next
-          return token
+          return self.next
         end
 
         return nil
@@ -42,8 +40,7 @@ module Lrama
         a = []
 
         while token_types.include?(current_type)
-          a << current_token
-          self.next
+          a << self.next
         end
 
         raise "No token is consumed. #{token_types}" if a.empty?
diff --git a/tool/lrama/lib/lrama/state.rb b/tool/lrama/lib/lrama/state.rb
index b868035e1a..6632bafecc 100644
--- a/tool/lrama/lib/lrama/state.rb
+++ b/tool/lrama/lib/lrama/state.rb
@@ -1,11 +1,11 @@
 require "lrama/state/reduce"
-require "lrama/state/shift"
+require "lrama/state/reduce_reduce_conflict"
 require "lrama/state/resolved_conflict"
+require "lrama/state/shift"
+require "lrama/state/shift_reduce_conflict"
 
 module Lrama
   class State
-    Conflict = Struct.new(:symbols, :reduce, :type, keyword_init: true)
-
     attr_reader :id, :accessing_symbol, :kernels, :conflicts, :resolved_conflicts,
                 :default_reduction_rule, :closure, :items
     attr_accessor :shifts, :reduces
@@ -101,6 +101,10 @@ module Lrama
       @term_transitions
     end
 
+    def transitions
+      term_transitions + nterm_transitions
+    end
+
     def selected_term_transitions
       term_transitions.select do |shift, next_state|
         !shift.not_selected
@@ -144,6 +148,10 @@ module Lrama
       end
     end
 
+    def has_conflicts?
+      [email protected]?
+    end
+
     def sr_conflicts
       @conflicts.select do |conflict|
         conflict.type == :shift_reduce
diff --git a/tool/lrama/lib/lrama/state/reduce_reduce_conflict.rb b/tool/lrama/lib/lrama/state/reduce_reduce_conflict.rb
new file mode 100644
index 0000000000..0a0e4dc20a
--- /dev/null
+++ b/tool/lrama/lib/lrama/state/reduce_reduce_conflict.rb
@@ -0,0 +1,9 @@
+module Lrama
+  class State
+    class ReduceReduceConflict < Struct.new(:symbols, :reduce1, :reduce2, keyword_init: true)
+      def type
+        :reduce_reduce
+      end
+    end
+  end
+end
diff --git a/tool/lrama/lib/lrama/state/shift_reduce_conflict.rb b/tool/lrama/lib/lrama/state/shift_reduce_conflict.rb
new file mode 100644
index 0000000000..f80bd5f352
--- /dev/null
+++ b/tool/lrama/lib/lrama/state/shift_reduce_conflict.rb
@@ -0,0 +1,9 @@
+module Lrama
+  class State
+    class ShiftReduceConflict < Struct.new(:symbols, :shift, :reduce, keyword_init: true)
+      def type
+        :shift_reduce
+      end
+    end
+  end
+end
diff --git a/tool/lrama/lib/lrama/states.rb b/tool/lrama/lib/lrama/states.rb
index cf26416a37..d27c5411ea 100644
--- a/tool/lrama/lib/lrama/states.rb
+++ b/tool/lrama/lib/lrama/states.rb
@@ -102,43 +102,27 @@ module Lrama
     end
 
     def direct_read_sets
-      h = {}
-
-      @direct_read_sets.each do |k, v|
-        h[k] = bitmap_to_terms(v)
+      @direct_read_sets.transform_values do |v|
+        bitmap_to_terms(v)
       end
-
-      return h
     end
 
     def read_sets
-      h = {}
-
-      @read_sets.each do |k, v|
-        h[k] = bitmap_to_terms(v)
+      @read_sets.transform_values do |v|
+        bitmap_to_terms(v)
       end
-
-      return h
     end
 
     def follow_sets
-      h = {}
-
-      @follow_sets.each do |k, v|
-        h[k] = bitmap_to_terms(v)
+      @follow_sets.transform_values do |v|
+        bitmap_to_terms(v)
       end
-
-      return h
     end
 
     def la
-      h = {}
-
-      @la.each do |k, v|
-        h[k] = bitmap_to_terms(v)
+      @la.transform_values do |v|
+        bitmap_to_terms(v)
       end
-
-      return h
     end
 
     private
@@ -452,7 +436,7 @@ module Lrama
 
             # Can resolve only when both have prec
             unless shift_prec && reduce_prec
-              state.conflicts << State::Conflict.new(symbols: [sym], reduce: reduce, type: :shift_reduce)
+              state.conflicts << State::ShiftReduceConflict.new(symbols: [sym], shift: shift, reduce: reduce)
               next
             end
 
@@ -501,16 +485,21 @@ module Lrama
 
     def compute_reduce_reduce_conflicts
       states.each do |state|
-        a = []
+        count = state.reduces.count
 
-        state.reduces.each do |reduce|
-          next if reduce.look_ahead.nil?
+        for i in 0...count do
+          reduce1 = state.reduces[i]
+          next if reduce1.look_ahead.nil?
 
-          intersection = a & reduce.look_ahead
-          a += reduce.look_ahead
+          for j in (i+1)...count do
+            reduce2 = state.reduces[j]
+            next if reduce2.look_ahead.nil?
 
-          if !intersection.empty?
-            state.conflicts << State::Conflict.new(symbols: intersection.dup, reduce: reduce, type: :reduce_reduce)
+            intersection = reduce1.look_ahead & reduce2.look_ahead
+
+            if !intersection.empty?
+              state.conflicts << State::ReduceReduceConflict.new(symbols: intersection, reduce1: reduce1, reduce2: reduce2)
+            end
           end
         end
       end
diff --git a/tool/lrama/lib/lrama/states/item.rb b/tool/lrama/lib/lrama/states/item.rb
index 5c3696cc7b..823ccc72e1 100644
--- a/tool/lrama/lib/lrama/states/item.rb
+++ b/tool/lrama/lib/lrama/states/item.rb
@@ -12,20 +12,56 @@ module Lrama
         rule.id
       end
 
+      def empty_rule?
+        rule.empty_rule?
+      end
+
+      def number_of_rest_symbols
+        rule.rhs.count - position
+      end
+
+      def lhs
+        rule.lhs
+      end
+
       def next_sym
         rule.rhs[position]
       end
 
+      def next_next_sym
+        rule.rhs[position + 1]
+      end
+
+      def previous_sym
+        rule.rhs[position - 1]
+      end
+
       def end_of_rule?
         rule.rhs.count == position
       end
 
+      def beginning_of_rule?
+        position == 0
+      end
+
+      def start_item?
+        rule.id == 0 && position == 0
+      end
+
       def new_by_next_position
         Item.new(rule: rule, position: position + 1)
       end
 
-      def previous_sym
-        rule.rhs[position - 1]
+      def symbols_before_dot
+        rule.rhs[0...position]
+      end
+
+      def symbols_after_dot
+        rule.rhs[position..-1]
+      end
+
+      def to_s
+        "#{lhs.id.s_value}: #{display_name}"
       end
 
       def display_name
diff --git a/tool/lrama/lib/lrama/states_reporter.rb b/tool/lrama/lib/lrama/states_reporter.rb
index d3dbe6b1b4..0d805829eb 100644
--- a/tool/lrama/lib/lrama/states_reporter.rb
+++ b/tool/lrama/lib/lrama/states_reporter.rb
@@ -14,13 +14,13 @@ module Lrama
 
     private
 
-    def _report(io, grammar: false, states: false, itemsets: false, lookaheads: false, solved: false, verbose: false)
+    def _report(io, grammar: false, states: false, itemsets: false, lookaheads: false, solved: false, counterexamples: false, verbose: false)
       # TODO: Unused terms
       # TODO: Unused rules
 
       report_conflicts(io)
       report_grammar(io) if grammar
-      report_states(io, itemsets, lookaheads, solved, verbose)
+      report_states(io, itemsets, lookaheads, solved, counterexamples, verbose)
     end
 
     def report_conflicts(io)
@@ -71,7 +71,11 @@ module Lrama
       io << "\n\n"
     end
 
-    def report_states(io, itemsets, lookaheads, solved, verbose)
+    def report_states(io, itemsets, lookaheads, solved, counterexamples, verbose)
+      if counterexamples
+        cex = Counterexamples.new(@states)
+      end
+
       @states.states.each do |state|
         # Report State
         io << "State #{state.id}\n\n"
@@ -194,6 +198,27 @@ module Lrama
           io << "\n" if !state.resolved_conflicts.empty?
         end
 
+        if counterexamples && state.has_conflicts?
+          # Report counterexamples
+          examples = cex.compute(state)
+          examples.each do |example|
+            label0 = example.type == :shift_reduce ? "shift/reduce"  : "reduce/reduce"
+            label1 = example.type == :shift_reduce ? "Shift derivation"  : "First Reduce derivation"
+            label2 = example.type == :shift_reduce ? "Reduce derivation" : "Second Reduce derivation"
+
+            io << "    #{label0} conflict on token #{example.conflict_symbol.id.s_value}:\n"
+            io << "        #{example.path1_item.to_s}\n"
+            io << "        #{example.path2_item.to_s}\n"
+            io << "      #{label1}\n"
+            example.derivations1.render_strings_for_report.each do |str|
+              io << "        #{str}\n"
+            end
+            io << "      #{label2}\n"
+            example.derivations2.render_strings_for_report.each do |str|
+              io << "        #{str}\n"
+            end
+          end
+        end
 
         if verbose
           # Report direct_read_sets
diff --git a/tool/lrama/lib/lrama/type.rb b/tool/lrama/lib/lrama/type.rb
new file mode 100644
index 0000000000..fe5ff74058
--- /dev/null
+++ b/tool/lrama/lib/lrama/type.rb
@@ -0,0 +1,4 @@
+module Lrama
+  class Type < Struct.new(:id, :tag, keyword_init: true)
+  end
+end
diff --git a/tool/lrama/lib/lrama/version.rb b/tool/lrama/lib/lrama/version.rb
index 54eea75bfd..3f2eb3b9d4 100644
--- a/tool/lrama/lib/lrama/version.rb
+++ b/tool/lrama/lib/lrama/version.rb
@@ -1,3 +1,3 @@
 module Lrama
-  VERSION = "0.5.3".freeze
+  VERSION = "0.5.4".freeze
 end
diff --git a/tool/lrama/template/bison/yacc.c b/tool/lrama/template/bison/yacc.c
index 61d23d506b..8f57984ef3 100644
--- a/tool/lrama/template/bison/yacc.c
+++ b/tool/lrama/template/bison/yacc.c
@@ -1220,26 +1220,30 @@ yydestruct (const char *yymsg,
 
 <%- if output.error_recovery -%>
 #ifndef YYMAXREPAIR
-# define YYMAXREPAIR 3
+# define YYMAXREPAIR(<%= output.parse_param_name %>) (3)
 #endif
 
-enum repair_type {
+#ifndef YYERROR_RECOVERY_ENABLED
+# define YYERROR_RECOVERY_ENABLED(<%= output.parse_param_name %>) (1)
+#endif
+
+enum yy_repair_type {
   insert,
   delete,
   shift,
 };
 
-struct repair {
-  enum repair_type type;
+struct yy_repair {
+  enum yy_repair_type type;
   yysymbol_kind_t term;
 };
-typedef struct repair repair;
+typedef struct yy_repair yy_repair;
 
-struct repairs {
+struct yy_repairs {
   /* For debug */
   int id;
   /* For breadth-first traversing */
-  struct repairs *next;
+  struct yy_repairs *next;
   YYPTRDIFF_T stack_length;
   /* Bottom of states */
   yy_state_t *states;
@@ -1248,10 +1252,10 @@ struct repairs {
   /* repair length */
   int repair_length;
   /*  */
-  struct repairs *prev_repair;
-  struct repair repair;
+  struct yy_repairs *prev_repair;
+  struct yy_repair repair;
 };
-typedef struct repairs repairs;
+typedef struct yy_repairs yy_repairs;
 
 struct yy_term {
   yysymbol_kind_t kind;
@@ -1260,12 +1264,12 @@ struct yy_term {
 };
 typedef struct yy_term yy_term;
 
-struct repair_terms {
+struct yy_repair_terms {
   int id;
   int length;
   yy_term terms[];
 };
-typedef struct repair_terms repair_terms;
+typedef struct yy_repair_terms yy_repair_terms;
 
 static void
 yy_error_token_initialize (yysymbol_kind_t yykind, YYSTYPE * const yyvaluep, YYLTYPE * const yylocationp<%= output.user_formals %>)
@@ -1280,11 +1284,11 @@ switch (yykind)
   YY_IGNORE_MAYBE_UNINITIALIZED_END
 }
 
-static repair_terms *
-yy_create_repair_terms(repairs *reps)
+static yy_repair_terms *
+yy_create_repair_terms(yy_repairs *reps<%= output.user_formals %>)
 {
-  repairs *r = reps;
-  repair_terms *rep_terms;
+  yy_repairs *r = reps;
+  yy_repair_terms *rep_terms;
   int count = 0;
 
   while (r->prev_repair)
@@ -1293,7 +1297,7 @@ yy_create_repair_terms(repairs *reps)
     r = r->prev_repair;
   }
 
-  rep_terms = (repair_terms *) malloc (sizeof (repair_terms) + sizeof (yy_term) * count);
+  rep_terms = (yy_repair_terms *) YYMALLOC (sizeof (yy_repair_terms) + sizeof (yy_term) * count);
   rep_terms->id = reps->id;
   rep_terms->length = count;
 
@@ -1309,46 +1313,46 @@ yy_create_repair_terms(repairs *reps)
 }
 
 static void
-yy_print_repairs(repairs *reps)
+yy_print_repairs(yy_repairs *reps<%= output.user_formals %>)
 {
-  repairs *r = reps;
+  yy_repairs *r = reps;
 
-  fprintf (stderr,
+  YYDPRINTF ((stderr,
         "id: %d, repair_length: %d, repair_state: %d, prev_repair_id: %d\n",
-        reps->id, reps->repair_length, *reps->state, reps->prev_repair->id);
+        reps->id, reps->repair_length, *reps->state, reps->prev_repair->id));
 
   while (r->prev_repair)
   {
-    fprintf (stderr, "%s ", yysymbol_name (r->repair.term));
+    YYDPRINTF ((stderr, "%s ", yysymbol_name (r->repair.term)));
     r = r->prev_repair;
   }
 
-  fprintf (stderr, "\n");
+  YYDPRINTF ((stderr, "\n"));
 }
 
 static void
-yy_print_repair_terms(repair_terms *rep_terms)
+yy_print_repair_terms(yy_repair_terms *rep_terms<%= output.user_formals %>)
 {
   for (int i = 0; i < rep_terms->length; i++)
-    fprintf (stderr, "%s ", yysymbol_name (rep_terms->terms[i].kind));
+    YYDPRINTF ((stderr, "%s ", yysymbol_name (rep_terms->terms[i].kind)));
 
-  fprintf (stderr, "\n");
+  YYDPRINTF ((stderr, "\n"));
 }
 
 static void
-yy_free_repairs(repairs *reps)
+yy_free_repairs(yy_repairs *reps<%= output.user_formals %>)
 {
   while (reps)
     {
-      repairs *r = reps;
+      yy_repairs *r = reps;
       reps = reps->next;
-      free (r->states);
-      free (r);
+      YYFREE (r->states);
+      YYFREE (r);
     }
 }
 
 static int
-yy_process_repairs(repairs *reps, yysymbol_kind_t token)
+yy_process_repairs(yy_repairs *reps, yysymbol_kind_t token)
 {
   int yyn;
   int yystate = *reps->state;
@@ -1417,22 +1421,22 @@ yyrecover_errlab:
   return 0;
 }
 
-static repair_terms *
-yyrecover(yy_state_t *yyss, yy_state_t *yyssp, int yychar)
+static yy_repair_terms *
+yyrecover(yy_state_t *yyss, yy_state_t *yyssp, int yychar<%= output.user_formals %>)
 {
   yysymbol_kind_t yytoken = YYTRANSLATE (yychar);
-  repair_terms *rep_terms = YY_NULLPTR;
+  yy_repair_terms *rep_terms = YY_NULLPTR;
   int count = 0;
 
-  repairs *head = (repairs *) malloc (sizeof (repairs));
-  repairs *current = head;
-  repairs *tail = head;
+  yy_repairs *head = (yy_repairs *) YYMALLOC (sizeof (yy_repairs));
+  yy_repairs *current = head;
+  yy_repairs *tail = head;
   YYPTRDIFF_T stack_length = yyssp - yyss + 1;
 
   head->id = count;
   head->next = 0;
   head->stack_length = stack_length;
-  head->states = (yy_state_t *) malloc (sizeof (yy_state_t) * (stack_length));
+  head->states = (yy_state_t *) YYMALLOC (sizeof (yy_state_t) * (stack_length));
   head->state = head->states + (yyssp - yyss);
   YYCOPY (head->states, yyss, stack_length);
   head->repair_length = 0;
@@ -1456,14 +1460,14 @@ yyrecover(yy_state_t *yyss, yy_state_t *yyssp, int yychar)
             {
               if (yyx != YYSYMBOL_YYerror)
                 {
-                  if (current->repair_length + 1 > YYMAXREPAIR)
+                  if (current->repair_length + 1 > YYMAXREPAIR(<%= output.parse_param_name %>))
                     continue;
 
-                  repairs *new = (repairs *) malloc (sizeof (repairs));
+                  yy_repairs *new = (yy_repairs *) YYMALLOC (sizeof (yy_repairs));
                   new->id = count;
                   new->next = 0;
                   new->stack_length = stack_length;
-                  new->states = (yy_state_t *) malloc (sizeof (yy_state_t) * (stack_length));
+                  new->states = (yy_state_t *) YYMALLOC (sizeof (yy_state_t) * (stack_length));
                   new->state = new->states + (current->state - current->states);
                   YYCOPY (new->states, current->states, current->state - current->states + 1);
                   new->repair_length = current->repair_length + 1;
@@ -1474,7 +1478,7 @@ yyrecover(yy_state_t *yyss, yy_state_t *yyssp, int yychar)
                   /* Process PDA assuming next token is yyx */
                   if (! yy_process_repairs (new, yyx))
                     {
-                      free (new);
+                      YYFREE (new);
                       continue;
                     }
 
@@ -1484,18 +1488,18 @@ yyrecover(yy_state_t *yyss, yy_state_t *yyssp, int yychar)
 
                   if (yyx == yytoken)
                     {
-                      rep_terms = yy_create_repair_terms (current);
-                      fprintf (stderr, "repair_terms found. id: %d, length: %d\n", rep_terms->id, rep_terms->length);
-                      yy_print_repairs (current);
-                      yy_print_repair_terms (rep_terms);
+                      rep_terms = yy_create_repair_terms (current<%= output.user_args %>);
+                      YYDPRINTF ((stderr, "repair_terms found. id: %d, length: %d\n", rep_terms->id, rep_terms->length));
+                      yy_print_repairs (current<%= output.user_args %>);
+                      yy_print_repair_terms (rep_terms<%= output.user_args %>);
 
                       goto done;
                     }
 
-                  fprintf (stderr,
+                  YYDPRINTF ((stderr,
                         "New repairs is enqueued. count: %d, yystate: %d, yyx: %d\n",
-                        count, yystate, yyx);
-                  yy_print_repairs (new);
+                        count, yystate, yyx));
+                  yy_print_repairs (new<%= output.user_args %>);
                 }
             }
         }
@@ -1505,11 +1509,11 @@ yyrecover(yy_state_t *yyss, yy_state_t *yyssp, int yychar)
 
 done:
 
-  yy_free_repairs(head);
+  yy_free_repairs(head<%= output.user_args %>);
 
   if (!rep_terms)
     {
-      fprintf (stderr, "repair_terms not found\n");
+      YYDPRINTF ((stderr, "repair_terms not found\n"));
     }
 
   return rep_terms;
@@ -1586,7 +1590,7 @@ YYLTYPE yylloc = yyloc_default;
   /* The locations where the error started and ended.  */
   YYLTYPE yyerror_range[3];
 <%- if output.error_recovery -%>
-  repair_terms *rep_terms = 0;
+  yy_repair_terms *rep_terms = 0;
   yy_term term_backup;
   int rep_terms_index;
   int yychar_backup;
@@ -1726,32 +1730,35 @@ yybackup:
   /* Not known => get a lookahead token if don't already have one.  */
 
 <%- if output.error_recovery -%>
-  if (yychar == YYEMPTY && rep_terms)
+  if (YYERROR_RECOVERY_ENABLED(<%= output.parse_param_name %>))
     {
-
-      if (rep_terms_index < rep_terms->length)
-        {
-          YYDPRINTF ((stderr, "An error recovery token is used\n"));
-          yy_term term = rep_terms->terms[rep_terms_index];
-          yytoken = term.kind;
-          yylval = term.value;
-          yylloc = term.location;
-          yychar = yytranslate_inverted[yytoken];
-          YY_SYMBOL_PRINT ("Next error recovery token is", yytoken, &yylval, &yylloc<%= output.user_args %>);
-          rep_terms_index++;
-        }
-      else
+      if (yychar == YYEMPTY && rep_terms)
         {
-          YYDPRINTF ((stderr, "Error recovery is completed\n"));
-          yytoken = term_backup.kind;
-          yylval = term_backup.value;
-          yylloc = term_backup.location;
-          yychar = yychar_backup;
-          YY_SYMBOL_PRINT ("Next token is", yytoken, &yylval, &yylloc<%= output.user_args %>);
-
-          free (rep_terms);
-          rep_terms = 0;
-          yychar_backup = 0;
+
+          if (rep_terms_index < rep_terms->length)
+            {
+              YYDPRINTF ((stderr, "An error recovery token is used\n"));
+              yy_term term = rep_terms->terms[rep_terms_index];
+              yytoken = term.kind;
+              yylval = term.value;
+              yylloc = term.location;
+              yychar = yytranslate_inverted[yytoken];
+              YY_SYMBOL_PRINT ("Next error recovery token is", yytoken, &yylval, &yylloc<%= output.user_args %>);
+              rep_terms_index++;
+            }
+          else
+            {
+              YYDPRINTF ((stderr, "Error recovery is completed\n"));
+              yytoken = term_backup.kind;
+              yylval = term_backup.value;
+              yylloc = term_backup.location;
+              yychar = yychar_backup;
+              YY_SYMBOL_PRINT ("Next token is", yytoken, &yylval, &yylloc<%= output.user_args %>);
+
+              YYFREE (rep_terms);
+              rep_terms = 0;
+              yychar_backup = 0;
+            }
         }
     }
 <%- end -%>
@@ -1980,27 +1987,28 @@ yyerrorlab:
 `-------------------------------------------------------------*/
 yyerrlab1:
 <%- if output.error_recovery -%>
-  {
-    rep_terms = yyrecover (yyss, yyssp, yychar);
-    if (rep_terms)
-      {
-        for (int i = 0; i < rep_terms->length; i++)
-          {
-            yy_term *term = &rep_terms->terms[i];
-            yy_error_token_initialize (term->kind, &term->value, &term->location<%= output.user_args %>);
-          }
+  if (YYERROR_RECOVERY_ENABLED(<%= output.parse_param_name %>))
+    {
+      rep_terms = yyrecover (yyss, yyssp, yychar<%= output.user_args %>);
+      if (rep_terms)
+        {
+          for (int i = 0; i < rep_terms->length; i++)
+            {
+              yy_term *term = &rep_terms->terms[i];
+              yy_error_token_initialize (term->kind, &term->value, &term->location<%= output.user_args %>);
+            }
 
-        yychar_backup = yychar;
-        /* Can be packed into (the tail of) rep_terms? */
-        term_backup.kind = yytoken;
-        term_backup.value = yylval;
-        term_backup.location = yylloc;
-        rep_terms_index = 0;
-        yychar = YYEMPTY;
+          yychar_backup = yychar;
+          /* Can be packed into (the tail of) rep_terms? */
+          term_backup.kind = yytoken;
+          term_backup.value = yylval;
+          term_backup.location = yylloc;
+          rep_terms_index = 0;
+          yychar = YYEMPTY;
 
-        goto yybackup;
-      }
-  }
+          goto yybackup;
+        }
+    }
 <%- end -%>
   yyerrstatus = 3;      /* Each real token shifted decrements this.  */